Fix nuget push on tag creation (#4)

Author: TWissing

.github/workflows/build-and-release.yml

@@ -37,7 +37,7 @@ jobs:
         name: packages
         path: '**/*.nupkg'
     - name: Push to nuget.org
-      if: github.ref == 'refs/heads/main'
+      if: startsWith(github.ref, 'refs/tags/v')
       run: dotnet nuget push **/*.nupkg --source https://api.nuget.org/v3/index.json --api-key ${NUGET_API_KEY}
       env:
         NUGET_API_KEY: ${{ secrets.NUGET_API_KEY }}