[Bug] Switching between light mode and dark mode in playground overwrites source markdown

[pugtooth]

Initial checklist

• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected packages and versions

Milkdown Playgroundv7.3.0

Link to runnable example

No response

Steps to reproduce

Type anything into the editor, switch between light modes, and the source text will be reset to default text.

Expected behavior

You keep your text (sorry for lame response, but I feel like this is a given)

Actual behavior

The preview will not be effected, but the source text will be reset to the default text.

Runtime

Chrome

OS

Linux

Build and bundle tools

No response