bug.yml: remind users to `brew update`

.github/ISSUE_TEMPLATE/bug.yml

@@ -6,6 +6,12 @@ body:
   - type: markdown
     attributes:
       value: Please note we will close your issue without comment if you do not fill out the issue checklist below and provide ALL the requested information. If you repeatedly fail to use the issue template, we will block you from ever submitting issues to Homebrew again.
+  - type: checkboxes
+    attributes:
+      description: Please verify that you've followed this step.
+      options:
+        - label: I did `brew update` and am still able to reproduce my issue.
+          required: true
   - type: textarea
     attributes:
       render: shell