Move `finished_loading?` to `wait_for_requests`

What does this MR do?

Moves finished_loading? to wait_for_requests and removes now unnecessary finished_loading? calls.

This should make tests more stable and help mitigate issues such as #224446 (closed)

Also quarantine two tests due to: #225303 (closed)

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team