add jdk 21 to workflows

Author: GGoetzelmann

.github/workflows/bootjar_testing.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        java: [17]
+        java: [17, 21]
 
     steps:
       - name: Checkout code

.github/workflows/gradle.yml

@@ -19,7 +19,7 @@ jobs:
       matrix:
         operating-system: [ubuntu-latest, macOS-latest]
         # Use both LTS releases and latest one for tests
-        jdk: [ 17 ]
+        jdk: [ 17, 21 ]
     steps:
     - name: Checkout repo
       uses: actions/checkout@v4