Add JDK 21 to test workflow

.github/workflows/ant.yml

@@ -42,7 +42,7 @@ jobs:
     needs: build
     strategy: 
       matrix: 
-        jdk: [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
+        jdk: [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21]
         goal: [javacCurrent]
         include:
           - jdk: 11
@@ -56,10 +56,19 @@ jobs:
         uses: actions/checkout@v3
       
       - name: Set up JDK ${{ matrix.jdk }}
+        if: ${{ matrix.jdk != 21 }}
         uses: actions/setup-java@v3
         with:
           java-version: ${{ matrix.jdk }}
           distribution: 'zulu'
+      
+      - name: Set up JDK 21-ea
+        if: ${{ matrix.jdk == 21 }}
+        uses: oracle-actions/setup-java@v1
+        with:
+          website: jdk.java.net
+          release: 21
+          version: latest
           
       - name: Install Ant
         run: |