Upgrade wrapper-validation-action to gradle/actions/wrapper-validation@v4

The old gradle/wrapper-validation-action@v1 was silently failing on all
PR runs (works on push-to-main but not on PR merge commits). The modern
replacement is gradle/actions/wrapper-validation which is actively
maintained by Gradle.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: pyricau

.github/workflows/main.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - uses: gradle/wrapper-validation-action@v1
+      - uses: gradle/actions/wrapper-validation@v4
 
   checks:
     runs-on: ubuntu-latest