chore: use latest Java LTS version (21) in CI tests

- update the setup-java action to v4
- add Java 21 to the Java version matrix
- update the JDK distribution to Eclipse Temurin (formerly AdoptOpenJDK)

.github/workflows/maven-ci.yml

@@ -12,16 +12,17 @@ jobs:
     name: "Build on Java ${{ matrix.java }}"
     strategy:
       matrix:
-        java: [8, 11, 16]
+        java: [8, 11, 17, 21]
     runs-on: ubuntu-latest
     steps:
     - name: "Checkout sources"
       uses: actions/checkout@v2
     - name: "Set up Java"
-      uses: actions/setup-java@v2
+      uses: actions/setup-java@v4
       with:
         java-version: ${{ matrix.java }}
-        distribution: "adopt"
+        distribution: "temurin"
+        cache: 'maven'
     - name: "Get Maven dependencies from cache"
       uses: actions/cache@v2
       with:
@@ -40,10 +41,10 @@ jobs:
     - name: "Checkout sources"
       uses: actions/checkout@v2
     - name: "Setup Java"
-      uses: actions/setup-java@v2
+      uses: actions/setup-java@v4
       with:
-        java-version: 11
-        distribution: "adopt"
+        java-version: 21
+        distribution: "temurin"
         server-id: ossrh
         server-username: OSSRH_USERNAME
         server-password: OSSRH_PASSWORD