update gradle-publish.yml to use JDK 21

Author: RyanHecht

.github/workflows/gradle-publish.yml

@@ -30,10 +30,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up JDK 17
+    - name: Set up JDK 21
       uses: actions/setup-java@v4
       with: 
-        java-version: '17'
+        java-version: '21'
         distribution: 'temurin'
         server-id:  github # Value of the distributionManagement/repository/id field of the pom.xml
         settings-path: ${{ github. workspace }} # location for the settings.xml file