Adds wait_for_requests to protect_branch call

What does this MR do?

This MR adds wait_for_requests call to the protect_branch method in order to prevent transient failure #196521 (closed)

closes #196521 (closed)

Note, the use of wait_for_requests may cause failures of tests when executing in headed mode under certain circumstances, namely if the execution is happening in a background workspace.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

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

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

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

Closes #196521 (closed)