[hotfix][ci] Polish ci concurrency group to avoid warning message

This closes apache#3241.

.github/workflows/flink_cdc.yml

@@ -30,8 +30,17 @@ on:
       - 'docs/**'
       - 'README.md'
 
+# Concurrency strategy:
+#   github.workflow: distinguish this workflow from others
+#   github.event_name: distinguish `push` event from `pull_request` event
+#   github.event.number: set to the number of the pull request if `pull_request` event
+#   github.run_id: otherwise, it's a `push` or `schedule` event, only cancel if we rerun the workflow
+#
+# Reference:
+#   https://docs.github.com/en/actions/using-jobs/using-concurrency
+#   https://docs.github.com/en/actions/learn-github-actions/contexts#github-context
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
+  group: ${{ github.workflow }}-${{ github.event_name }}-${{ github.event.number || github.run_id }}
   cancel-in-progress: true
 
 env:
@@ -151,7 +160,7 @@ jobs:
           cache: 'maven'
 
       - name: Set Maven 3.8.6
-        uses: stCarolas/setup-maven@v4.5
+        uses: stCarolas/setup-maven@v5
         with:
           maven-version: 3.8.6