Disallow failures for passing builds

[pirj]

1. Disallow failures for Rails 6.1 on Ruby 3.0

Both are pretty stable, and the build actually passes
https://github.com/rspec/rspec-rails/runs/3771356606

2. Turn pending test to a regular one for Rails 5.2

ActiveSupport::Cache::RedisCacheStore's usage of safe navigation was fixed in Rails 5.2.5:
https://github.com/rails/rails/blob/v5.2.4.3/activesupport/lib/active_support/cache/redis_cache_store.rb#L323
https://github.com/rails/rails/blob/v5.2.5/activesupport/lib/active_support/cache/redis_cache_store.rb#L323

In ActionDispatch::Request::Session it was fixed, too:
https://github.com/rails/rails/blob/v5.2.4.3/actionpack/lib/action_dispatch/request/session.rb#L96
https://github.com/rails/rails/blob/v5.2.5/actionpack/lib/action_dispatch/request/session.rb#L96

Our pending was actually failing (since the test was passing) for some while:

 Failures:

  1) RSpec::Rails::ViewExampleGroup#view is accessible to configuration-level hooks FIXED
     Expected pending '
          Rails 5.2.4.2 has a syntax error in ActionDispatch::Request::Session.
          (A &. usage which does not work in 2.2.10)
          It has been fixed but not released, this spec will not pass until that
          has been released.
        ' to fail. No error was raised.
     # ./spec/rspec/rails/example/view_example_group_spec.rb:254

❓ Do we need to keep the build for 5-2-stable?