Added action for php 8.1 build

.github/workflows/build.php81.ant.yml

@@ -0,0 +1,22 @@
+name: CI (Ant, PHP 8.1)
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup PHP with PECL extension
+        uses: shivammathur/setup-php@v2
+        with:
+            php-version: '8.1'
+            extensions: imagick, swoole      
+      - name: Set up JDK 11
+        uses: actions/setup-java@v2
+        with:
+            java-version: '11'
+            distribution: 'adopt'
+      - name: Build with Ant
+        run: ant -noinput -buildfile build.ant.xml