Incorrect report of `incorrect delimiter` error when unicode characters are used beforehand

[Iorvethe]

Describe the bug This is best understood with a screen-cast as show here using the following file content.

$𝒪$ _text_ text

The steps to reproduce are:

1. Open the file
2. Move the delimiter to the end
3. Undo and redo the operation multiple times of moving the delimiter
4. Error pops up

Another way to trigger it is to change the 𝒪 by a O, as show here.

Package/Software version:

tinymist extension version: v0.11.1. Get it by tinymist --version in terminal.

tinymist
Build Timestamp:     1980-01-01T00:00:00.000000000Z
Build Git Describe:  VERGEN_IDEMPOTENT_OUTPUT
Commit SHA:          VERGEN_IDEMPOTENT_OUTPUT
Commit Date:         None
Commit Branch:       None
Cargo Target Triple: x86_64-unknown-linux-gnu
Typst Version:       0.11.1

tinymist -V

tinymist 0.11.20