CICD : Don't execute NuGet push on any branch other than master

Author: vittorelli

.github/workflows/dotnet.yml

@@ -32,7 +32,7 @@ jobs:
       # publish Core on version change
       - name: publish Core on version change
         id: publish_core
-        if: success()
+        if: github.ref == 'refs/heads/master' && success()
         uses: Clivar/publish-nuget@master
         with:
           # Filepath of the project to be packaged, relative to root of repository