Fix InlineCodeHighlight styling and unknown-language fallback

[antonymilne]

Hello! A vizro user noticed some weird behaviour that I've eventually traced back to two small bugs in dmc.InlineCodeHighlight. This PR hopefully fixes both 🤞 I haven't updated any tests so please let me know if that's required!

Here's an example app to show the bugs.

When you click the button you'll see:

• Style change of inline code: it uses default styling at first (because there's missing dmc-code.css) and when you click the button, the CodeHighlight block loads and injects dmc-code.css, so the inline code style suddenly changes.
• Italic VAR in ENV_VAR_NAME: unknown languages were highlighted as markdown, so you get unwanted syntax highlighting instead of plain text

Here's what happens after the fix: the style of the inline code is correct from the beginning (no italic for unknown language) and doesn't change when you click the button.

[AnnMarieW]

Hi @antonymilne

Thanks so much for reporting the issue and providing the fix! 🚀

This works great. We don't have a test for this, as we typically focus on tests for dash callbacks or props that are only in dmc and not Mantine. If you would like to add a test, it would be welcomed, but not required.

Just need to add a changelog entry before merging.

Thanks again!

[antonymilne]

Hi @AnnMarieW, no worries! I've added a changelog now. I thought for a while about tests and couldn't figure out a very valuable way to do it for these changes so didn't add any, hope that's ok. 🙂

Do you know when this might be released?

[AnnMarieW]

Thanks @antonymilne 💃

I should be able to get the next release done this week.