[CI] fix CI skipped on main (#13527)

.github/workflows/pr-gate.yml

@@ -14,10 +14,10 @@ jobs:
   pr-gate:
     # 1. for commits on main: no gating needed
     # 2. for workflow_dispatch: this can only be triggered by users with write access
-    if: github.event_name == 'pull_request'
     runs-on: ubuntu-latest
     steps:
       - name: Fetch latest PR info
+        if: github.event_name == 'pull_request'
         id: pr
         uses: actions/github-script@v7
         with:
@@ -33,6 +33,7 @@ jobs:
             core.setOutput("user", pr.data.user.login);
 
       - name: Log PR info
+        if: github.event_name == 'pull_request'
         run: |
           echo "===== PR Info ====="
           echo "PR Event: ${{ github.event_name }}"
@@ -44,13 +45,13 @@ jobs:
           echo "==================="
 
       - name: Block draft PR
-        if: fromJson(steps.pr.outputs.draft)
+        if: github.event_name == 'pull_request' && fromJson(steps.pr.outputs.draft)
         run: |
           echo "PR is draft. Blocking CI."
           exit 1
 
       - name: Require run-ci label (optional)
-        if: inputs.require-run-ci == true
+        if:  github.event_name == 'pull_request' && inputs.require-run-ci == true
         run: |
           labels='${{ steps.pr.outputs.labels }}'
           if [[ "${{ contains(fromJson(steps.pr.outputs.labels), 'run-ci') }}" == "false" ]]; then
@@ -59,6 +60,7 @@ jobs:
           fi
 
       - name: Enforce rate limit for low-permission actors (optional)
+        if: github.event_name == 'pull_request' && inputs.rate-limit-hours > 0
         uses: actions/github-script@v7
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}