Add a test to assert branch-alias is well defined (#1610)

Author: jderusse

.github/workflows/branch_alias.yml

@@ -38,7 +38,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "1.21-dev"
+            "dev-master": "1.20-dev"
         }
     }
 }