ci(branch protection): adds input for configuration

.github/workflows/branch-protection-warning.yml

@@ -1,23 +1,30 @@
 name: "Check if merging to 'main' from 'release' branch"
 
 on:
- pull_request:
-   branches: # These should be primary branch names.
-    - main
-    - master
+  workflow_call:
+    inputs:
+      primary_branch:
+        description: 'The name of the primary branch this workflow will run on.'
+        required: false
+        type: string
+        default: 'main'
+
+permissions:
+  contents: read
 
 jobs:
- protect-primary-branch:
-   runs-on: ubuntu-latest
+  protect-primary-branch:
+    runs-on: ubuntu-latest
 
-   # To prevent a merge on failure, branch protection must be enabled in GitHub. If branch
-   # protection is disabled, this will fail with a red X but nothing prevents you from merging
-   # anyway.
-   steps:
-     - name: Check merge branch
-       if: github.event.pull_request.base.ref == 'main'
-       run: |
-         if [ "${{ github.event.pull_request.head.ref }}" != "release" ]; then
-           echo "Merges to 'main' are only allowed from the 'release' branch."
-           exit 1
-         fi 
+    # To prevent a merge on failure, branch protection must be enabled in GitHub. If branch
+    # protection is disabled, this will fail with a red X but nothing prevents you from merging
+    # anyway.
+    steps:
+      - name: Check merge branch
+        if: github.event.pull_request.base.ref == ${{ inputs.primary_branch }}
+        run: |
+        if [ "${{ github.event.pull_request.head.ref }}" != "release" ]; then
+          echo "Merges to '${{ inputs.primary_branch }}' are only allowed from the 'release' branch."
+          exit 1
+        fi
+        echo "Success!"