[TASK] Prepare release of version 9.0.0

Closes #1326

Author: oliverklee

composer.json

@@ -61,7 +61,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-main": "9.0.x-dev"
+            "dev-main": "9.1.x-dev"
         }
     },
     "scripts": {