Update build-pr.yml

Add java 21 and downgrade wrapper validation as it is the last release version

Author: OneLiteFeather

.github/workflows/build-pr.yml

@@ -12,11 +12,11 @@ jobs:
       - name: Checkout Repository
         uses: actions/checkout@v4
       - name: Validate Gradle Wrapper
-        uses: gradle/actions/wrapper-validation@v4
+        uses: gradle/actions/wrapper-validation@v3
       - name: Setup Java
         uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
       - name: Build on ${{ matrix.os }}
-        run: ./gradlew clean build -x test
+        run: ./gradlew clean build -x test