Fix flaky test in code_suggestions_client_spec.rb

What does this MR do and why?

Currently the tests in ee/lib/gitlab/llm/ai_gateway/code_suggestions_client.rb occasionally fail with the following error:

     WebMock::NetConnectNotAllowedError:
       Real HTTP connections are disabled. Unregistered request: POST https://cloud.gitlab.com/auth/v1/code/user_access_token with headers {'Accept'=>'*/*', 'Accept-Encoding'=>'gzip;q=1.0,deflate;q=0.6,identity;q=0.3', 'Authorization'=>'Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiJ9.eyJqdGkiOiI5Yjk3MjU0Ni0zOWVjLTQ0YTMtYTBlNy01OTg0Y2RjODIwMzYiLCJhdWQiOiJnaXRsYWItYWktZ2F0ZXdheSIsInN1YiI6bnVsbCwiaXNzIjoiaHR0cDovL2xvY2FsaG9zdCIsImlhdCI6MTcxODIwNzc3MiwibmJmIjoxNzE4MjA3NzY3LCJleHAiOjE3MTgyMTEzNzIsImdpdGxhYl9yZWFsbSI6InNlbGYtbWFuYWdlZCIsInNjb3BlcyI6W119.MW_aQMOe3KTUkghHAqTDnRaQ-bcoJ7VP5OQhpNqadsMq8bIKisIEoIlO6QiShJs5UEbdTUFleqLqwnspx2fkfnQQPsPpQnL_hAGmp-7zieQEK44fql0C2f4BYDTdNrARhe8YTlCCnuJWUSvnZDFLgL-ARl3yursvaHOL2-DLs-3fzAJC0NqFN1OaVDskd3Leq23oVGuF_xu5nAw34CWWqHnvXMpGMfC0kYGvxrzbAgppDjdwGY9mYwCu_oEmbn1u6v_IRriOdUT5qGxwBeR1Q1VIa3kUiTRddtw6rmYp0h2V2JQXiUDfD8DPblN7OevDON-IHGXUXdmXnXbJu2T7IQ', 'Content-Type'=>'application/json', 'User-Agent'=>'Ruby', 'X-Gitlab-Authentication-Type'=>'oidc', 'X-Gitlab-Global-User-Id'=>'1l5HJGcgrJb0JDYkH3mhdnNGy0aUwb1HqikSkiCltjw=', 'X-Gitlab-Host-Name'=>'localhost', 'X-Gitlab-Instance-Id'=>'uuid-not-set', 'X-Gitlab-Realm'=>'self-managed', 'X-Gitlab-Version'=>'17.1.0', 'X-Request-Id'=>'1f93fd6d5eb6c42e6a43d3305404e84e'}

The problem is that there is a state leak between spec files that is order dependent. Further details are explained in #467246 (comment 1950115093).

The quick fix is to clear the necessary memoizations when :with_cloud_connector is used. However, it's noted in #467246 (comment 1950115093) that we should consider a more robust long term solution.

Resolves #467246 (closed) and related issues.

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Before	After

How to set up and validate locally

1. Before checking out this branch, you can reproduce the error by running the following:

bundle exec rspec --order defined ee/spec/requests/api/internal/ai/x_ray/scan_spec.rb:197 ee/spec/lib/gitlab/llm/ai_gateway/code_suggestions_client_spec.rb:104

2. After checking out this branch, re-run the command above. Observe there is no error.

Related to #467246 (closed)