### 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
print_verbose("Build Android project using gradle command: " + String("\n") + build_command + " " + join_list(cmdline, String(" ")));
		if (should_sign) {
			if (p_debug) {
				String debug_keystore = p_preset->get("keystore/debug");
				String debug_password = p_preset->get("keystore/debug_password");
				String debug_user = p_preset->get("keystore/debug_user");
				if (debug_keystore.is_empty()) {
					debug_keystore = EDITOR_GET("export/android/debug_keystore");
					debug_password = EDITOR_GET("export/android/debug_keystore_pass");
					debug_user = EDITOR_GET("export/android/debug_keystore_user");
				}
				if (debug_keystore.is_relative_path()) {
					debug_keystore = OS::get_singleton()->get_resource_dir().path_join(debug_keystore).simplify_path();
				}
				if (!FileAccess::exists(debug_keystore)) {
					add_message(EXPORT_MESSAGE_ERROR, TTR("Code Signing"), TTR("Could not find keystore, unable to export."));
					return ERR_FILE_CANT_OPEN;
				}
				cmdline.push_back("-Pdebug_keystore_file=" + debug_keystore); 
				cmdline.push_back("-Pdebug_keystore_alias=" + debug_user); 
				cmdline.push_back("-Pdebug_keystore_password=" + debug_password); 
			} else {
				
				String release_keystore = p_preset->get("keystore/release");
				String release_username = p_preset->get("keystore/release_user");
				String release_password = p_preset->get("keystore/release_password");
				if (release_keystore.is_relative_path()) {
					release_keystore = OS::get_singleton()->get_resource_dir().path_join(release_keystore).simplify_path();
				}