### Godot version

any version after 74458b6

### System information

Linux x64, but likely irrelevant

### Issue description

OpenXR action maps are not properly exported in recent builds of Godot 4: the `.res` file is small and does no longer seem to contain anything of use. In-game, no actions are passed on to OpenXR (obviously).

I bisected the issue down to https://github.com/godotengine/godot/commit/74458b6e9bed0f28db3374c7406eacbcf4b09b9d, which was merged in #70377.

### Steps to reproduce

1. Delete any previous export files (`.godot/exported/*/*.pkg`)
2. Perform an export (I did one for Android, but it likely works with anything)
3. Observe OpenXR actions not working in the export (error spam 'sync_action_sets: Condition "active_sets.size() == 0"'), and the exported action map file being very small (`.godot/exported/*/*.pkg`, from a few tens of kilobytes down to 296 bytes)

### Minimal reproduction project

Any OpenXR project can be used, such as https://github.com/BastiaanOlij/godot4_openxr_demo
if (!p_force_save && customize_resources_plugins.is_empty() && customize_scenes_plugins.is_empty()) {
		return p_path; 
	}
	
	if (export_cache.has(p_path)) {
		FileExportCache &fec = export_cache[p_path];
		if (fec.saved_path.is_empty() || FileAccess::exists(fec.saved_path)) {
			
			uint64_t mod_time = FileAccess::get_modified_time(p_path);
			if (fec.source_modified_time == mod_time) {
				
				fec.used = true;
				return fec.saved_path.is_empty() ? p_path : fec.saved_path;
			}
			String md5 = FileAccess::get_md5(p_path);
			if (FileAccess::exists(p_path + ".import")) {
				
				md5 += FileAccess::get_md5(p_path + ".import");
			}