Only upload artifacts for certain operating systems in the matrix

.github/workflows/build.yml

@@ -53,7 +53,7 @@ jobs:
 
     - name: Release
       uses: softprops/action-gh-release@v1
-      if: startsWith(github.ref, 'refs/tags/')
+      if: ${{ startsWith(github.ref, 'refs/tags/') && (os.matrix == 'windows-2019' || os.matrix == 'macos-10.15' || os.matrix == 'ubuntu-16.04') }}
       with:
         prerelease: ${{ !startsWith(github.ref, 'refs/tags/v') || contains(github.ref, '-pre') }}
         files: ${{ github.event.repository.name }}-${{ steps.osname.outputs.lowercase }}.zip