Downgrade CI jobs to JDK 23

CI has to wait for the PRs which handle the JDK SM removal.

.github/workflows/main.yml

@@ -428,11 +428,11 @@ jobs:
         run: ant -quiet -Dcluster.config=$CLUSTER_CONFIG test -Dtest.includes=NoTestsJustBuild
 
       # 13-14 min for javadoc; JDK version must be synced with nb-javac
-      - name: Set up JDK 24-ea for javadoc
+      - name: Set up JDK 23 for javadoc
         if: env.test_javadoc == 'true' && success()
         uses: actions/setup-java@v4
         with:
-          java-version: 24-ea 
+          java-version: 23 
           distribution: ${{ env.DEFAULT_JAVA_DISTRIBUTION }}
 
       - name: Build javadoc
@@ -833,7 +833,7 @@ jobs:
     timeout-minutes: 50
     strategy:
       matrix:
-        java: [ '17', '21', '24-ea' ]
+        java: [ '17', '21', '23' ]
         exclude:
           - java: ${{ github.event_name == 'pull_request' && 'nothing' || '21' }}
       fail-fast: false
@@ -1493,7 +1493,7 @@ jobs:
     timeout-minutes: 60
     strategy:
       matrix:
-        java: [ '17', '21', '24-ea' ]
+        java: [ '17', '21', '23' ]
         exclude:
           - java: ${{ github.event_name == 'pull_request' && 'nothing' || '21' }}
       fail-fast: false