[SPARK-29079][INFRA] Enable GitHub Action on PR

This PR enables GitHub Action on PRs.

So far, we detect JDK11 compilation error after merging.
This PR aims to prevent JDK11 compilation error at PR stage.

No.

Manual. See the GitHub Action on this PR.

Closes #25786 from dongjoon-hyun/SPARK-29079.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: DB Tsai <[email protected]>

Author: dongjoon-hyun

.github/workflows/branch-2.4.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches:
     - branch-2.4
+  pull_request:
+    branches:
+    - branch-2.4
 
 jobs:
   build: