Update GHA Workflow to latest versions

We need Java 11 (for its JDK) and Java 21 for build tools.

Author: jonahgraham

.github/workflows/ci.yml

@@ -9,18 +9,20 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         submodules: true
-    - name: Set up JDK 11
-      uses: actions/setup-java@v4
+    - name: Set up JDKs
+      uses: actions/setup-java@v5
       with:
-        java-version: 11
         distribution: temurin
+        java-version: |
+          11
+          21
     - name: Setup Maven
       run: echo "MAVEN_OPTS='-Xmx2048m'" > ~/.mavenrc
     - name: Cache maven repo
-      uses: actions/cache@v4
+      uses: actions/cache@v5
       env:
         cache-name: cache-maven-repo
       with: