Remove mirror username from URI in E2E tests

The UI tells the user not to include the username in the URI for mirrors, however, the E2E tests include the username for mirrors. We should be testing the typical user workflow.

https://gitlab.com/gitlab-org/gitlab/-/blob/eb98728bab78c3f7e29b065be8d265942463860e/qa/qa/specs/features/ee/browser_ui/3_create/repository/pull_mirroring_over_ssh_with_key_spec.rb#L31-31