Add "-Pjava21Home" to stage docker step (#39181)

Follow what we did for javadoc step

Author: Abacn

.github/workflows/build_release_candidate.yml

@@ -281,7 +281,7 @@ jobs:
         with:
           distribution: 'temurin'
           java-version: |
-            17
+            21
             11
       - name: Install Python 3.10
         uses: actions/setup-python@v5
@@ -300,7 +300,7 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USER }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
       - name: Push docker images
-        run: ./gradlew ${{ matrix.images_to_publish.gradle_task }} -PisRelease -Pdocker-pull-licenses -Pprune-images ${{ matrix.images_to_publish.include_skip_flags }} -Pdocker-tag=${{ github.event.inputs.RELEASE }}rc${{ github.event.inputs.RC }} --no-daemon --no-parallel
+        run: ./gradlew ${{ matrix.images_to_publish.gradle_task }} -PisRelease -Pdocker-pull-licenses -Pprune-images ${{ matrix.images_to_publish.include_skip_flags }} -Pdocker-tag=${{ github.event.inputs.RELEASE }}rc${{ github.event.inputs.RC }} -Pjava21Home=$JAVA_HOME_21_X64 --no-daemon --no-parallel
 
   beam_site_pr:
     if:  ${{ fromJson(github.event.inputs.STAGE).beam_site_pr == 'yes'}}