Dollar signs cause syntax coloring to fail

First, thank you for picking up and modernizing my favorite Markdown editor!

Interesting things happen to the the syntax coloring when you use dollar signs. Try the following:

```
[^6]: Raspberry Pi 5 is ~$45-95 (1GB vs. 8GB), PSU is ~$15, case is $25, USB hub is $10, 64GB card is $20.

Notice how this text is now grayed out (or whatever the theme renders it as)
```
I have had to resort to always writing dollar signs as `$` in the meantime to get around this since unless the dollar signs are in pairs, it will do this — but this is clearly not optimal 😄

Reproduce the issue with the Markdown footnote example containing unmatched dollar signs, then trace the syntax-coloring or Markdown-rendering entry point used by the macOS editor. No file or test is named in the issue; done means dollar signs in ordinary text no longer cause the surrounding text to become incorrectly grayed out.

Written by the indexing model from the issue text.