### Godot version

4.1.dev (dc625bcbfc5b587ba8867481ee7a1f6a567c25d0)

### System information

Mageia 9, Linux

### Issue description

When importing a project in current `master`, the following error is raised for each asset that gets imported:
```
Attempting to parent and popup a dialog that already has a parent.
```

It seems to be raised once per asset, caused by the progress dialog.

CC @bruvzg

### Steps to reproduce

- Import a new project in Godot that contains importable assets, e.g. https://github.com/RPicster/godot4-demo-desert-light

### Minimal reproduction project

See above.
ERR_MAIN_THREAD_GUARD;
	switch (p_what) {
		case NOTIFICATION_POSTINITIALIZE: {
			initialized = true;
			_invalidate_theme_cache();
			_update_theme_item_cache();
		} break;
		case NOTIFICATION_PARENTED: {
			theme_owner->assign_theme_on_parented(this);
		} break;
		case NOTIFICATION_UNPARENTED: {
			theme_owner->clear_theme_on_unparented(this);
		} break;
		case NOTIFICATION_ENTER_TREE: {
			bool embedded = false;
			{
				embedder = get_embedder();
				if (embedder) {
					embedded = true;
					if (!visible) {
						embedder = nullptr;