Small fix in github action, missed in #105, see there for details

Author: abelbraaksma

.github/workflows/publish.yaml

@@ -22,6 +22,7 @@ jobs:
       - name: Run dotnet build (release, for nuget)
         # see issue #105
         # very important, since we use cmd scripts, the default is psh, and a bug prevents errorlevel to bubble
+        shell: cmd
         run: ./build.cmd
       - name: Nuget publish
         # skip-duplicate ensures that the 409 error received when the package was already published,