Update maven.yml

Author: brendandburns

.github/workflows/maven.yml

@@ -26,8 +26,7 @@ jobs:
     name: Java ${{ matrix.java }} Maven Test on ${{ matrix.os }}
     strategy:
       matrix:
-        # Test against the LTS Java versions. TODO: add JDK18 when it becomes available.
-        java: [ 11.0.x, 17.0.x ]
+        java: [ 11.0.x, 17.0.x, 21.0.x ]
         os: [ macos-latest, windows-latest, ubuntu-latest ]
     runs-on: ${{ matrix.os }}
     steps: