docs: *-regressions.rst: Add colon to regzbot commands

Use colon as command terminator everywhere for consistency, even though
it's not strictly necessary. That way it will also match regzbot's
reference documentation.

Link: https://gitlab.com/knurd42/regzbot/-/blob/main/docs/reference.md


Reviewed-by: Thorsten Leemhuis <linux@leemhuis.info>
Signed-off-by: "Nícolas F. R. A. Prado" <nfraprado@collabora.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20240311-regzbot-fixes-v2-1-98c1b6ec0678@collabora.com>