chore(deps): update gradle/actions action to v6 (#5630)

Author: renovate[bot]

.github/workflows/verify-flatpak.yml

@@ -31,7 +31,7 @@ jobs:
           distribution: temurin
           java-version: 21
 
-      - uses: gradle/actions/setup-gradle@v4
+      - uses: gradle/actions/setup-gradle@v6
 
       - name: Generate flatpak-sources.json
         run: |