a11y - Colour contrast issues (hyperlinks)

[trallard]

Unfortunately, the accessibility test failures are real. The update to the kitchen sink brought in some new links. These new links do not meet color contrast thresholds (WCAG AA). Some screen shots below:

Light mode

In light mode, the link color is #0a7d91.

(same goes for versionchanged, deprecated, and versionremoved admonitions)

Dark mode

In dark mode, the link color is #3fb1c5 and it has enough contrast with all of the admonition backgrounds except one.

Originally posted by @gabalafou in #2190 (comment)