Allow for non-spaced links in internally-defined Markdown-links

[jhlegarreta]

According to
https://www.markdownguide.org/basic-syntax/#formatting-the-first-part-of-the-link

the whitespace between the first and second set of brackets for internally-defined is not a requirement.

The regex patterns to check for internally-defined Markdown links in here seem to require a whitespace.

The relevant warning raised in an incubator repository:
https://github.com/carpentries-incubator/SDC-BIDS-dMRI/runs/2401702149?check_suite_focus=true#step:16:29

is no longer raised if a whitespace is introduced. However, if Markdown accepts both syntaxes, would it be possible to update the lesson-check.py script to account for them?

If "proper" Markdown does require a whitespace, please let me know and I will close the issue and add a whitespace in the mentionned repository.

Thanks.