Writing a user config file in GitHub actions job fails test

When running the [(commented-out) test](https://github.com/Structed/godot-playfab/blob/db0ca9f1e1ee170080394fa8ed21bd7a22778a34/addons/godot-playfab/test/unit/PlayFabClientConfig/test_PlayFabClientConfigLoader.gd#L13) in the GitHub Actions workflow, the test fails.

See also: https://github.com/croconut/godot-tester/issues/19