Update JDK version to 21 in CI workflow

Changed the Java setup steps in multiOSReleases.yml to use JDK 21 instead of JDK 17 for building and testing. This ensures compatibility with newer Java features and aligns with updated project requirements.

.github/workflows/multiOSReleases.yml

@@ -123,10 +123,10 @@ jobs:
 
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
-          java-version: "17"
+          java-version: "21"
           distribution: "temurin"
 
       - uses: gradle/actions/setup-gradle@4d9f0ba0025fe599b4ebab900eb7f3a1d93ef4c2 # v5.0.0
@@ -244,10 +244,10 @@ jobs:
           toolchain: stable
           targets: ${{ (matrix.platform == 'macos-15' || matrix.platform == 'macos-15-intel') && 'aarch64-apple-darwin,x86_64-apple-darwin' || '' }}
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00 # v4.7.1
         with:
-          java-version: "17"
+          java-version: "21"
           distribution: "temurin"
 
       - name: Build Java backend with JLink