Update github workflow for java 21

Author: bertrik

.github/workflows/gradle.yml

@@ -22,10 +22,10 @@ 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'
 
     # Configure Gradle for optimal use in GiHub Actions, including caching of downloaded dependencies.
@@ -55,10 +55,10 @@ 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'
 
     # Generates and submits a dependency graph, enabling Dependabot Alerts for all project dependencies.