All captions should use Markdown figure caption syntax

As part of reviewing episodes for #468 I noticed in some places figure captions are being included manually using HTML `

` tags - for example

https://github.com/carpentries-incubator/python-intermediate-development/blob/73f53de20a30028ea80a1c5c87742763a08eef1c/episodes/14-collaboration-using-git.md?plain=1#L312-L314

https://github.com/carpentries-incubator/python-intermediate-development/blob/1dfe85705edda426afa4e7f257b980cffd316997/episodes/14-collaboration-using-git.md?plain=1#L367-L370

It's not clear if this is required because of use of HTML tags in the caption text, but if not using the built-in figure caption syntax would probably be preferable.

Tasks:

- [x] Check if figure captions can handle embedded HTML / Markdown.