Update nugetGallery.yml

Avoid running the action multiple times per release.

Author: darkl

.github/workflows/nugetGallery.yml

@@ -2,6 +2,7 @@ name: NuGet Gallery NuGet generation
 
 on:
   release:
+    types: [published]
     branches:
       - master
 
@@ -32,4 +33,4 @@ jobs:
       - name: Push generated package to GitHub registry
         run: |
           cd src\netstandard          
-          nuget push .\out\*.nupkg -Source "GPR" -SkipDuplicate
+          nuget push .\out\*.nupkg -Source "GPR" -SkipDuplicate