Test PHP 8.0 with lowest dependencies (#8878)

.github/workflows/continuous-integration.yml

@@ -55,6 +55,10 @@ jobs:
             os: macos-latest
             dependencies: locked
             experimental: false
+          - php-version: 8.0
+            dependencies: lowest
+            os: ubuntu-latest
+            experimental: true
           - php-version: 8.0
             dependencies: highest-ignore
             os: ubuntu-latest
@@ -125,5 +129,5 @@ jobs:
         if: "matrix.php-version == '8.0'"
         run: |
           bin/composer remove --dev symfony/phpunit-bridge --ignore-platform-reqs
-          bin/composer require phpunit/phpunit:^7.5 --ignore-platform-reqs
+          bin/composer require phpunit/phpunit:^7.5 --ignore-platform-reqs --with-dependencies
           vendor/bin/phpunit