ci: update GitHub Actions

Author: Samarium150

.github/workflows/Gradle CI.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       # Setup JDK
       - name: Setup Java JDK