docs: *-regressions.rst: unify quoting, add missing word

Quoting of the '"no regressions" rule' expression differs between
occurrences, sometimes being presented as '"no regressions rule"'. Unify
the quoting using the first form which seems semantically correct or is
at least used dominantly, albeit marginally.

One of the occurrences is obviously missing the 'rule' part -- add it.

Signed-off-by: Karel Balej <balejk@matfyz.cz>
Reviewed-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240328194342.11760-2-balejk@matfyz.cz