Fix flaky branch rules spec
What does this MR do and why?
ee/spec/requests/api/graphql/project/branch_rules_spec.rb
appears to
have failed in https://gitlab.com/gitlab-org/gitlab/-/jobs/6494504318
because the branch rule creation date was off by a second. It appears
that there was a copy and paste error here since the test was
comparing the wrong branch rule creation date.
Edited by Stan Hu