Merge branch 'ps/send-pack-unhide-error-in-atomic-push'

Merge branch 'ps/send-pack-unhide-error-in-atomic-push'

"git push --atomic --porcelain" used to ignore failures from the
other side, losing the error status from the child process, which
has been corrected.

* ps/send-pack-unhide-error-in-atomic-push:
  send-pack: gracefully close the connection for atomic push
  t5543: atomic push reports exit code failure
  send-pack: new return code "ERROR_SEND_PACK_BAD_REF_STATUS"
  t5548: add porcelain push test cases for dry-run mode
  t5548: add new porcelain test cases
  t5548: refactor test cases by resetting upstream
  t5548: refactor to reuse setup_upstream() function
  t5504: modernize test by moving heredocs into test bodies