Fix command palette TimeoutError error (#3321)

* Reinstate the import of TimeoutError from asyncio

Fixes #3320

It looks like eaa7496 smuggled this change
in and caused the command palette to cease to work correctly on any version
of Python before 3.11.

This should make it work on all Pythons from 3.7 onward again.

* Update the CHANGELOG

Author: davep

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## Unreleased
+
+### Fixed
+
+- Fixed the command palette crashing with a `TimeoutError` in any Python before 3.11 https://github.com/Textualize/textual/issues/3320
+
 ## [0.37.0] - 2023-09-15
 
 ### Added

src/textual/command.py

@@ -7,7 +7,7 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
-from asyncio import CancelledError, Queue, Task, wait, wait_for
+from asyncio import CancelledError, Queue, Task, TimeoutError, wait, wait_for
 from dataclasses import dataclass
 from functools import total_ordering
 from time import monotonic