Doc/git-{push,send-pack}: correct --sign= to --signed=

Doc/git-{push,send-pack}: correct --sign= to --signed=

Since we're about to touch the behavior of --signed=, do this as a
preparatory step.

The documentation mentions --sign=, and it works. But that's just
because it's an unambiguous abbreviation of --signed, which is how it is
actually implemented. This was added in commit 30261094 ("push: support
signing pushes iff the server supports it", 2015-08-19). Back when that
series was developed [1] [2], there were suggestions about both --sign=
and --signed=. The final implementation settled on --signed=, but some
of the documentation and commit messages ended up using --sign=.

The option is referred to as --signed= in Documentation/config.txt
(under push.gpgSign).

One could argue that we have promised --sign for two years now, so we
should implement it as an alias for --signed. (Then we might also
deprecate the latter, something which was considered already then.) That
would be a slightly more intrusive change.

This minor issue would only be a problem once we want to implement some
other option --signfoo, but the earlier we do this step, the better.

[1] v1-thread:
https://public-inbox.org/git/1439492451-11233-1-git-send-email-dborowitz@google.com/T/#u

[2] v2-thread:
https://public-inbox.org/git/1439998007-28719-1-git-send-email-dborowitz@google.com/T/#m6533a6c4707a30b0d81e86169ff8559460cbf6eb

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>