Fix AppVeyor tests

Author: dunglas

composer.json

@@ -74,7 +74,7 @@
         "symfony/framework-bundle": "^4.2",
         "symfony/mercure-bundle": "*",
         "symfony/messenger": "^4.2",
-        "symfony/phpunit-bridge": "^4.3.1",
+        "symfony/phpunit-bridge": "^4.3@dev",
         "symfony/routing": "^3.4 || ^4.0",
         "symfony/security-bundle": "^3.4 || ^4.0",
         "symfony/security-core": "^3.4 || ^4.0",