ci: update gradle/wrapper-validation-action to v4

The pinned SHA was running on Node 16, which the current GitHub runner
image (2.334.0) no longer supports, causing the Validation job to fail
on every PR. v4 runs on Node 20 and has an up-to-date Gradle checksum
list.

Author: symphony-enrico

.github/workflows/gradle-wrapper-validation.yml

@@ -9,4 +9,4 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: gradle/wrapper-validation-action@56b90f209b02bf6d1deae490e9ef18b21a389cd4
+      - uses: gradle/actions/wrapper-validation@v4