Run label check workflow only on label events and open pr event (#4830)

## **PR Description**
- Currently, `check-required-label` only runs when commits are added to
a PR, even if a maintainer has added labels, so the CI status remains
red until a commit is pushed after labels are added by a maintainer.
- I updated the workflows to run `check-required-label` only on label
events(add/remove) or open PR event.
- This will make PR status updates more accurate, so authors will be
able to see that tests and lint are passing by just checking the PR
status, and maintainers will easily know if the PR is ready for review.

Author: stefanhaller

.github/workflows/check-required-label.yml

@@ -0,0 +1,15 @@
+name: Check Required Labels
+
+on:
+  pull_request:
+    types: [opened, labeled, unlabeled]
+
+jobs:
+  check-required-label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: mheap/github-action-required-labels@v5
+        with:
+          mode: exactly
+          count: 1
+          labels: "ignore-for-release, feature, enhancement, bug, maintenance, docs, i18n, performance"

.github/workflows/ci.yml

@@ -175,15 +175,6 @@ jobs:
       - name: errors
         run: golangci-lint run
         if: ${{ failure() }}
-  check-required-label:
-    runs-on: ubuntu-latest
-    if: github.ref != 'refs/heads/master'
-    steps:
-      - uses: mheap/github-action-required-labels@v5
-        with:
-          mode: exactly
-          count: 1
-          labels: "ignore-for-release, feature, enhancement, bug, maintenance, docs, i18n, performance"
   upload-coverage:
     # List all jobs that produce coverage files
     needs: [unit-tests, integration-tests]