Nested bold/italic/code formatting sometimes doesn't format correctly

![image](https://github.com/user-attachments/assets/c16a0f0f-5bac-41b5-87a3-f9b2a2b45c79)


Neither of these display the correct formatting:
```
Wolfram`Chatbook`FormatChatOutput[ "**Step 1: Switch to the *main* branch**" ]
```

```
Wolfram`Chatbook`FormatChatOutput[ "**Step 1: Switch to the `main` branch**" ]
```