housekeeping: Reference required secrets

Author: glennawatson

.github/workflows/release.yml

@@ -17,3 +17,7 @@ jobs:
       productNamespacePrefix: "Splat"
       useVisualStudioPreview: false
       useMauiCheckDotNetTool: false
+      SIGN_CLIENT_USER_ID: ${{ secrets.SIGN_CLIENT_USER_ID }}
+      SIGN_CLIENT_SECRET: ${{ secrets.SIGN_CLIENT_SECRET }}
+      SIGN_CLIENT_CONFIG: ${{ secrets.SIGN_CLIENT_CONFIG }}
+      NUGET_API_KEY: ${{ secrets.NUGET_API_KEY }}