git-branchless-submit: when --pulling, compares against pull remote instead of push remote

[arxanas]

Description of the bug

In https://discord.com/channels/915309546984050709/915310626291740752/1098644284351197294, user hank points out that git-branchless-submit behaves strangely when setting pushRemote for an individual branch (rather than for the remote).

To set up:

1. Set up a pull remote and a push remote for the repository.
2. Create a branch foo tracking a branch on the pull remote. Ensure that no branch foo exists on the pull remote.
3. Set branch foo's push remote to the push remote for the repository (i.e. branch.foo.pushRemote).
4. Run git submit.

Expected behavior

The branch is not pushed since --create was not passed to git submit.

Actual behavior

The branch is pushed even though it doesn't exist on the push remote.

Version of rustc

No response

Automated bug report

No response

Version of git-branchless

No response

Version of git

No response