ci: main branch protection (#4443)

.github/workflows/main-protect.yml

@@ -0,0 +1,18 @@
+name: Main Branch Protection
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  check-branch:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check branch
+        run: |
+          if [[ ${GITHUB_HEAD_REF} != canary ]] && ! [[ ${GITHUB_HEAD_REF} =~ ^v[0-9]+\.[0-9]+\.[0-9]+-staging$ ]];
+          then
+            echo "Error: Pull request must come from 'canary' or 'v*.*.*-staging' branch"
+            exit 1
+          fi