### Godot version

3.5.1.stable, v4.0.beta.custom_build [0a87ead64]

### System information

Ubuntu 22.04.1

### Issue description

For example, if project has name "300spartans", we can't enter the "org.godotengine.300spartans" to "Unique Name" field. We get the error "Invalid package name: A digit cannot be the first character in a package segment". But , if we enter "org.godotengine.$genname", there will be no error message. When exporting, the name will be set as "org.godotengine.spartans" without "300" in beginning, but user will not be informed about it. I think, it is not very good. It may not be worth making changes to the source code, but mention it in the documentation.

### Steps to reproduce

See issue description.

### Minimal reproduction project

N/A
#define CLEANUP_AND_RETURN(m_err)                         \
	{                                                     \
		DirAccess::remove_file_or_error(tmp_export_path); \
		return m_err;                                     \
	}                                                     \
	((void)0)
	
	Error err = export_project_helper(p_preset, true, tmp_export_path, EXPORT_FORMAT_APK, true, p_debug_flags);
	if (err != OK) {
		CLEANUP_AND_RETURN(err);
	}
	List<String> args;
	int rv;
	String output;
	bool remove_prev = EDITOR_GET("export/android/one_click_deploy_clear_previous_install");
	String version_name = p_preset->get("version/name");
	String package_name = p_preset->get("package/unique_name");
	if (remove_prev) {
		if (ep.step(TTR("Uninstalling..."), 1)) {
			CLEANUP_AND_RETURN(ERR_SKIP);
		}
		print_line("Uninstalling previous version: " + devices[p_device].name);
		args.push_back("-s");
		args.push_back(devices[p_device].id);
		args.push_back("uninstall");
		args.push_back(get_package_name(package_name));
		output.clear();
		err = OS::get_singleton()->execute(adb, args, &output, &rv, true);
		print_verbose(output);
	}