add 21-ea to gh action build

Signed-off-by: Lukas Jungmann <lukas.jungmann@oracle.com>

.github/workflows/maven.yml

diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index 25376ac..29b8749 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2021 Contributors to the Eclipse Foundation
+# Copyright (c) 2021, 2023 Contributors to the Eclipse Foundation
 #
 # This program and the accompanying materials are made available under the
 # terms of the Eclipse Public License v. 2.0 which is available at
@@ -16,6 +16,10 @@
   pull_request:
   push:
 
+concurrency:
+  group: ${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     name: Test on JDK ${{ matrix.java_version }}
@@ -23,13 +27,13 @@
 
     strategy:
       matrix:
-        java_version: [ 11, 17-ea ]
+        java_version: [ 11, 17, 21-ea ]
 
     steps:
     - name: Checkout for build
-      uses: actions/checkout@v2.3.4
+      uses: actions/checkout@v3
     - name: Set up JDK
-      uses: actions/setup-java@v2
+      uses: actions/setup-java@v3
       with:
         distribution: 'zulu'
         java-version: ${{ matrix.java_version }}