Enable php8 in build matrix

Author: jaapio

.github/workflows/push.yml

@@ -64,17 +64,13 @@ jobs:
   phpunit:
     name: Unit tests for PHP version ${{ matrix.php-versions }} on ${{ matrix.operating-system }}
     runs-on: ${{ matrix.operating-system }}
-    continue-on-error: ${{ matrix.php-versions == '8.0' }}
     strategy:
       matrix:
         operating-system:
           - ubuntu-latest
           - windows-latest
           - macOS-latest
-        php-versions: ['7.2', '7.3', '7.4']
-        include:
-          - operating-system: ubuntu-latest
-            php-versions: '8.0'
+        php-versions: ['7.2', '7.3', '7.4', '8.0']
     env:
       extensions: mbstring
       key: cache-v1 # can be any string, change to clear the extension cache.