send-pack: run GPG after atomic push checking

send-pack: run GPG after atomic push checking

The refs update commands can be sent to the server side in two different
ways: GPG-signed or unsigned.  We should run these two operations in the
same "Finally, tell the other end!" code block, but they are seperated
by the "Clear the status for each ref" code block.  This will result in
a slight performance loss, because the failed atomic push will still
perform unnecessary preparations for shallow advertise and GPG-signed
commands buffers, and user may have to be bothered by the (possible) GPG
passphrase input when there is nothing to sign.

Add a new test case to t5534 to ensure GPG will not be called when the
GPG-signed atomic push fails.

Signed-off-by: Han Xin <hanxin.hx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>