Added a workflow to publish to pub.dev

Author: Ajay

.github/workflows/publish-on-merge.yml

@@ -4,7 +4,7 @@ version: 1.1.3
 homepage: https://github.com/ProjectAJ14/ns_firebase_utils
 
 environment:
-  sdk: ">=2.17.1 <3.0.0"
+  sdk: '>=2.17.1 <4.0.0'
 
 dependencies:
   flutter: