Use the same JDK 21 as ruby-builder and setup-ruby

Author: eregon

.github/workflows/build.yml

@@ -144,10 +144,8 @@ jobs:
     - run: echo $Env:Path
 
     - name: switch to Java 21 for verification
-      uses: actions/setup-java@v3
-      with:
-        distribution: 'zulu'
-        java-version: 21
+      run: echo "JAVA_HOME=${JAVA_HOME_21_X64:-${JAVA_HOME_21_arm64:-}}" >> "$GITHUB_ENV"
+      shell: bash
     - run: ruby --version
     - run: ruby -e 'raise unless RUBY_ENGINE == %{jruby}'
     - run: gem --version