use github token correctly.

Author: RossBugginsNHS

.github/workflows/stage-5-publish.yaml

@@ -222,7 +222,7 @@ jobs:
           dotnet nuget push \
           nhsnotifysupplier.${TEST_NUGET_VERSION}.nupkg \
           --source github \
-          --api-key ${GITHUB_TOKEN}
+          --api-key ${{ secrets.GITHUB_TOKEN }}
 
 ### Publish NPM