fix: handle missing NuGet API key in publish workflow

Author: Nonanti

.github/workflows/publish.yml

@@ -44,4 +44,12 @@ jobs:
       run: dotnet pack src/CodeContext.CLI/CodeContext.CLI.csproj --configuration Release --no-build -p:Version=${{ env.VERSION }} -o ./artifacts
 
     - name: Push to NuGet
-      run: dotnet nuget push ./artifacts/*.nupkg --api-key ${{ secrets.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate
+      env:
+        NUGET_API_KEY: ${{ secrets.NUGET_API_KEY }}
+      run: |
+        if [ -z "$NUGET_API_KEY" ]; then
+          echo "Warning: NUGET_API_KEY not set. Skipping NuGet push."
+          echo "To enable automatic publishing, add NUGET_API_KEY to repository secrets."
+          exit 0
+        fi
+        dotnet nuget push ./artifacts/*.nupkg --api-key $NUGET_API_KEY --source https://api.nuget.org/v3/index.json --skip-duplicate