Update branch-alias to 2.x-dev (#37)

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>
Co-authored-by: Pascal Birchler <pascalb@google.com>

Author: github-actions[bot]

composer.json

@@ -60,5 +60,10 @@
             "@phpunit",
             "@behat"
         ]
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-main": "2.x-dev"
+        }
     }
 }