Merge pull request #357 from mkurz/test_java21_9.1.x

[9.1.x] Also test against Java 21

Author: mkurz

.github/workflows/build-test.yml

@@ -37,7 +37,7 @@ jobs:
       - "check-docs"
     uses: playframework/.github/.github/workflows/cmd.yml@v3
     with:
-      java: 17, 11
+      java: 21, 17, 11
       scala: 2.13.x, 3.x
       cmd: |
         sbt ++$MATRIX_SCALA test