heroku_san: heroku_san uses wrong heroku account only when pushing git

Possibly related to: https://github.com/fastestforward/heroku_san/pull/86.

I can run this command with problem:

 git push heroku-staging develop:master

But if I try to run

rake staging deploy

I get this error below.

So I run the manual command to deploy above. And then I run

rake staging migrate

git update-ref refs/heroku_san/deploy HEAD^{commit}
git push git@heroku.com:staging-someapp.git  refs/heroku_san/deploy:refs/heads/master

 !  Your account blah@blah.com does not have access to staging-someapp.
 !
 !  SSH Key Fingerprint: blah blah

fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
git update-ref -d refs/heroku_san/deploy
rake aborted!
Command failed with status (128): [git push git@heroku.com:staging-someapp....]
/Users/justin/.rvm/gems/ruby-2.0.0-p451@someapp/gems/heroku_san-4.3.2/lib/heroku_san/git.rb:23:in `git_push'