Update rspec-rails gem to 6.0.1 version

What does this MR do and why?

This MR updates rspec-rails gem from 5.0.1 to 6.0.1.

Changelog: https://github.com/rspec/rspec-rails/blob/main/Changelog.md

It provides support for Rails 7 and fixes some of the tests that are failing for Rails 7 at the moment. For example, https://gitlab.com/gitlab-org/gitlab/-/jobs/3664192677 job fails due to missing ActionMailer::DeliveryJob and https://github.com/rspec/rspec-rails/issues/2531 states that it has been fixed in 6.x version.

It's also fixes ActionView::MissingTemplate: issues in views specs.

Since the gem is for development, test environments only, we can rely on tests and get away without gradually update to 5.0.1 -> 5.1.2 -> 6.0.1