docs: use inline-code instead of default role

docs: use inline-code instead of default role

A single backtick escaped string in Sphinx refers to the "default role"
which is vague, and in practice ends up producing the HTML cite-element.
That's almost certainly not what these uses wanted.

A bunch of these would probably be better served using appropriate roles
instead of inline-code markup, but this is almost certainly what was
meant here instead. Let's not let perfect be the enemy of good here, and
just do what was intended. Using the right roles everywhere is a big
task.

I usually don't do changes like these to the relnotes, but in this case
there were a *single* article that had these mistakes. I assume that was
an early bug in the script that generateg the relnotes. Let's patch it,
so we don't get misrendering if we change the default-role.

Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19494>