tests: test against upcoming symfony 6

.github/workflows/phpunit-symfony6.yml

@@ -0,0 +1,37 @@
+name: phpunit-symfony6
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: true
+      matrix:
+        os:
+          - ubuntu-latest
+        php:
+          - 8.0
+          - 8.1
+
+    name: php${{ matrix.php }} - symfony 6
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: xdebug
+
+      - name: Setup Problem Matches
+        run: |
+          echo "::add-matcher::${{ runner.tool_cache }}/php.json"
+          echo "::add-matcher::${{ runner.tool_cache }}/phpunit.json"
+      - name: Install dependencies
+        run: composer require symfony/http-foundation:6.0.x-dev && composer update
+
+      - name: Execute tests
+        run: vendor/bin/phpunit -v