[Contracts] update branch alias

Author: nicolas-grekas

composer.json

@@ -30,7 +30,7 @@
     "minimum-stability": "dev",
     "extra": {
         "branch-alias": {
-            "dev-main": "3.2-dev"
+            "dev-main": "3.3-dev"
         },
         "thanks": {
             "name": "symfony/contracts",