Currently tests only run on X11.64 platform.
But other platforms can be supported with a bit of effort.
Remove default bell sound as it does not play nicely with CI environment
that does not have sound card.
Gut was freezing on some integration tests. It was also entering an
infinite loop after exiting (even after closing Godot and VSCode) which
caused a `godot.log` file in app_userdata to keep growing until my hard
drive was full.
Fresh clones of this repo will need to install Gut using
gd-plug:
```
godot --no-window -s plug.gd install
```
Similar to how git submodules also need to be installed.
