git-verify-* doc: update mark-up of synopsis option descriptions

git-verify-* doc: update mark-up of synopsis option descriptions

To unify mark-up used in our documentation to a newer convention,
started by 22293895 (doc: apply synopsis simplification on git-clone
and git-init, 2024-09-24), update the documentation pages for 'git
verify-commit', 'git verify-tag', and 'git verify-pack' to

 * use [synopsis], not [verse] in the SYNOPSIS section
 * enclose `--option=<value>` in backquotes
 * do not describe non-option arguments in the OPTIONS section

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Helped-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>