Workflows tweaks

- use new `GITHUB_ACTIONS_HOMEBREW_MACOS_SELF_HOSTED` variable
- add some comments to explain Linux code

.github/workflows/dispatch-build-bottle.yml

@@ -29,7 +29,7 @@ jobs:
     timeout-minutes: 4320
     env:
       PATH: "/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"
-      GITHUB_ACTIONS_HOMEBREW_SELF_HOSTED: 1
+      GITHUB_ACTIONS_HOMEBREW_MACOS_SELF_HOSTED: 1
       GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
     steps:
       - name: ${{github.event.inputs.formula}}

.github/workflows/dispatch-rebottle.yml

@@ -30,7 +30,7 @@ jobs:
     timeout-minutes: 4320
     env:
       PATH: "/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin"
-      GITHUB_ACTIONS_HOMEBREW_SELF_HOSTED: 1
+      GITHUB_ACTIONS_HOMEBREW_MACOS_SELF_HOSTED: 1
       GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
       HOMEBREW_NO_BOTTLE_SOURCE_FALLBACK: 1
     steps:

.github/workflows/tests.yml

@@ -130,8 +130,9 @@ jobs:
         run: |
           if [ "$RUNNER_OS" = 'macOS' ]; then
             echo 'PATH=/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin' >> $GITHUB_ENV
-            echo 'GITHUB_ACTIONS_HOMEBREW_SELF_HOSTED=1' >> $GITHUB_ENV
+            echo 'GITHUB_ACTIONS_HOMEBREW_MACOS_SELF_HOSTED=1' >> $GITHUB_ENV
           else
+            # No PATH needed on Linux as set by Docker
             echo 'HOMEBREW_CORE_GIT_REMOTE=${{github.event.repository.html_url}}' >> $GITHUB_ENV
             echo 'HOMEBREW_FORCE_HOMEBREW_ON_LINUX=1' >> $GITHUB_ENV
           fi
@@ -152,6 +153,8 @@ jobs:
       - if: runner.os == 'macOS'
         run: brew test-bot --only-cleanup-before
 
+      # `brew doctor` won't work on Linux (yet)
+      # TODO: reenable this when possible.
       - if: runner.os == 'macOS'
         run: brew test-bot --only-setup