Always require spec_helper first in CI

What does this MR do?

Always require spec_helper first in CI, so we avoid loading fast_rspec_helper first. It's likely we need to load the whole Rails anyway.

How to reproduce the issue locally?

Run:

bundle exec rspec spec/lib/gitlab/robots_txt/parser_spec.rb spec/requests/robots_txt_spec.rb

How this will fix it?

The fix is essentially making it to run it this way:

bundle exec rspec -Ispec -rspec_helper spec/lib/gitlab/robots_txt/parser_spec.rb spec/requests/robots_txt_spec.rb

This is proven working by editing the above two files and rspec fail-fast will run those two tests in: https://gitlab.com/gitlab-org/gitlab/-/jobs/817155100

We can see that Gitlab::RobotsTxt::Parser runs first then Robots.txt Requests

Closes #249992 (closed)