Add missing symfony/deprecation-contracts requirement

Author: jderusse

composer.json

@@ -19,6 +19,7 @@
         "php": ">=7.2.5",
         "doctrine/event-manager": "~1.0",
         "doctrine/persistence": "^1.3|^2",
+        "symfony/deprecation-contracts": "^2.1",
         "symfony/polyfill-ctype": "~1.8",
         "symfony/polyfill-mbstring": "~1.0",
         "symfony/polyfill-php80": "^1.15",