Use Java 21 in gradle wrapper update action

Author: RaphiMC

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

@@ -10,5 +10,11 @@ jobs:
     steps:
       - name: Checkout Repository
         uses: actions/checkout@v4
+      - name: Set up JDK 21
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 21
+          check-latest: true
       - name: Update Gradle Wrapper
         uses: gradle-update/update-gradle-wrapper-action@v1