Bold text with percentage symbol failed to render

### Is this a hackmd.io issue?

- [x] Yes, the bug happens on https://hackmd.io
- [ ] No. If it's a self-hosted CodiMD instance, please fire up the issue in the repo of CodiMD: https://github.com/hackmdio/codimd

### Read our Official tutorial

It's on https://hackmd.io/c/tutorials/

或是中文版 https://hackmd.io/c/tutorials-tw/

### What's the problem

#### Current behaviour

> Screenshot (optional)

Provide steps to reproduce:

1. Go to 'hackmd.io/new' to create new note
2. Type some text with '%' symbol
3. Bold text '**60%**text'
4. See unexpected behavior: The bold mark `**` seems not parsed correctly. `**` showed in preview, and in editor the text not get bolded too.

note link / minimal reproducible example: https://hackmd.io/@ChenyHsu/ryoziO-Wee

#### Expected behaviour

The text quoted with `**` should rendered as bold.

#### Environment

I use HackMD on:

**Desktop**
- OS: Arch Linux x86_64
- Browser: firefox
- Browser Version: 138.0.1
- native: not flatpak or snap

#### Additional information
KDE kate text editor works for such case: