docs: prefer `Fixes:` over `Cc: mesa-stable`

`Fixes:` targets a specific commit and as such is much more precise and
useful than `Cc: mesa-stable`, so let's prefer it when applicable.

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5378>
1 file changed