[Bug] worktree prune --expires

Hi Team,

This is pretty much just a quibble, but the command parser for worktree prune --expires should really report when a timestamp is invalid. For example:

worktree prune --expires A:30 actually

actually appears to process the prune going back a very long time instead of reporting that A:30 isn't a good timestamp.

Experienced using git 2.29.2 in Cygwin - not my usual space and git 2.31.0 on NonStop.

I suspect that this should use the same timestamp parse as for other commands, although I also noticed that git log --since accepts the same syntactically awkward time. Am I missing something?

Thanks, Randall

-- Brief whoami:
 NonStop developer since approximately 211288444200000000
 UNIX developer since approximately 421664400
-- In my real life, I talk too much.