E2E test: dequarantine ssh mirror spec in gstg

What does this MR do and why?

Since gitlab-com/gl-infra/production#6621 (closed) is now resolved this spec can be de-quarantined. This spec was failing most of the time on staging and staging-canary due to a network configuration issue.

How to set up and validate locally

Values are in 1password Gitlab-QA:

canary staging

QA_LOG_LEVEL=debug QA_COOKIES=gitlab_canary=true GITLAB_QA_USER_AGENT=XXX GITLAB_USERNAME=gitlab-qa GITLAB_PASSWORD=XXX GITLAB_QA_ACCESS_TOKEN=XXX QA_GITLAB_URL=https://staging.gitlab.com bundle exec rspec qa/specs/features/ee/browser_ui/3_create/repository/pull_mirroring_over_ssh_with_key_spec.rb

staging

QA_LOG_LEVEL=debug GITLAB_QA_USER_AGENT=XXX GITLAB_USERNAME=gitlab-qa GITLAB_PASSWORD=XXX GITLAB_QA_ACCESS_TOKEN=XXX QA_GITLAB_URL=https://staging.gitlab.com bundle exec rspec qa/specs/features/ee/browser_ui/3_create/repository/pull_mirroring_over_ssh_with_key_spec.rb

MR acceptance checklist

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