workflows/tests: set timeout, fail fast using labels.

This adds support for using `CI-long-timeout` and `CI-no-fail-fast` to
set the timeout to 3 days (the current default) and make matrix jobs
not fail fast (the current default).

We could potentially explore more labels like this in order to further
customise how we run things in CI. For example, optionally passing
`--fail-fast`, `--skip-recursive-dependents` and potentially new options
to e.g. skip all dependent checking could all be options to allow us to
customise our CI usage.

This could also allow us to disable e.g. failing on a `brew audit`
failure so that we can start requiring green CI to be able to merge PRs.

The code here is a bit copy-paste for now but I wanted feedback on the
approach before spending more time on it. As-is the YAML linter I'm
using also complains about the types being incorrect (strings rather
than boolean/integer) so I'm interested if there's a workaround for that
too.

.github/workflows/tests.yml

@@ -1,7 +1,8 @@
 name: GitHub Actions CI
 on:
   push:
-    branches: master
+    branches:
+      - master
   pull_request:
 env:
   HOMEBREW_DEVELOPER: 1
@@ -13,9 +14,6 @@ jobs:
   tap_syntax:
     if: github.repository == 'Homebrew/homebrew-core'
     runs-on: ubuntu-latest
-    outputs:
-      run-tests: ${{ steps.check-labels.outputs.result }}
-      skip-arm-tests: ${{ steps.check-arm-labels.outputs.result }}
     env:
       HOMEBREW_SIMULATE_MACOS_ON_LINUX: 1
     steps:
@@ -45,8 +43,7 @@ jobs:
             fi
           done
 
-      - name: Check for CI-syntax-only label
-        id: check-labels
+      - name: Check for CI labels
         uses: actions/github-script@v3
         if: github.event_name == 'pull_request'
         with:
@@ -57,29 +54,43 @@ jobs:
               repo: context.repo.repo,
               pull_number: context.issue.number
             })
-            if (!labels.map(label => label.name).includes('CI-syntax-only')) {
-              console.log('No CI-syntax-only label found. Running tests.')
-              return true
-            }
-            console.log('CI-syntax-only label found. Skipping tests.')
+            const label_names = labels.map(label => label.name)
 
-      - name: Check for CI-force-arm label
-        id: check-arm-labels
-        uses: actions/github-script@v3
-        if: github.event_name == 'pull_request'
-        with:
-          github-token: ${{ secrets.GITHUB_TOKEN }}
-          script: |
-            const { data: { labels: labels } } = await github.pulls.get({
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              pull_number: context.issue.number
-            })
-            if (!labels.map(label => label.name).includes('CI-force-arm')) {
-              console.log('No CI-force-arm label found.')
-              return true
+            if (label_names.includes('CI-syntax-only')) {
+              console.log('CI-syntax-only label found. Skipping tests.')
+              console.log("::set-output name=run-tests::false");
+            }
+            else {
+              console.log('No CI-syntax-only label found. Running tests.')
+              console.log("::set-output name=run-tests::true");
+            }
+
+            if (label_names.includes('CI-no-fail-fast')) {
+              console.log('CI-no-fail-fast label found. Continue until all matrix builds have run.')
+              console.log("::set-output name=fail-fast::false");
+            }
+            else {
+              console.log('No CI-no-fail-fast label found. Fail on first failing matrix builds.')
+              console.log("::set-output name=fail-fast::true");
+            }
+
+            if (label_names.includes('CI-long-timeout')) {
+              console.log('CI-long-timeout label found. Setting long timeout.')
+              console.log("::set-output name=timeout-minutes::4320");
+            }
+            else {
+              console.log('No CI-long-timeout label found. Setting short timeout.')
+              console.log("::set-output name=timeout-minutes::60");
+            }
+
+            if (label_names.includes('CI-force-arm')) {
+              console.log('CI-force-arm label found. Running ARM builds.')
+              console.log("::set-output name=skip-arm-tests::false");
+            }
+            else {
+              console.log('No CI-force-arm label found. Skipping ARM builds.')
+              console.log("::set-output name=skip-arm-tests::true");
             }
-            console.log('CI-force-arm label found.')
 
   tests:
     needs: tap_syntax
@@ -87,9 +98,9 @@ jobs:
     strategy:
       matrix:
         version: ["11-arm64", "11", "10.15", "10.14"]
-      fail-fast: false
+      fail-fast: ${{ needs.tap_syntax.outputs.fail-fast }}
     runs-on: ${{ matrix.version }}
-    timeout-minutes: 4320
+    timeout-minutes: ${{ needs.tap_syntax.outputs.timeout-minutes }}
     env:
       PATH: "/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"
       HOMEBREW_DEVELOPER: 1
@@ -100,9 +111,7 @@ jobs:
       - name: Check whether ARM tests will be forced
         if: needs.tap_syntax.outputs.skip-arm-tests
         run: echo 'HOMEBREW_REQUIRE_BOTTLED_ARM=1' >> $GITHUB_ENV
-      - name: Force vendored Ruby on Catalina
-        if: matrix.version == '10.15'
-        run: echo 'HOMEBREW_FORCE_VENDOR_RUBY=1' >> $GITHUB_ENV
+
       - name: Set up Homebrew
         id: set-up-homebrew
         uses: Homebrew/actions/setup-homebrew@master