Improve pull request URL matching regex

Improve pull request URL matching regex

When git-request-pull output is pasted into a mail client instead of
mailed directly, the ref part of the pull URL may end up wrapped to the
next line.

Example: https://lore.kernel.org/r/294422a4-37b2-def5-5d32-8988f27c3a5b@gmail.com/

This change properly parses URLs both with and without newlines.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
(cherry picked from commit 8c229caa71d58e971708ac7ebdb02d6858cd2a4c)