Update troubleshooting section of doc/ci/merge_request_pipelines/pipelines_for_merged_results/index.md

What does this MR do?

The troubleshooting section of doc/ci/merge_request_pipelines/pipelines_for_merged_results/index.md describes how a feature flag can be checked and set. The description above the commands currently only says something about how to check a flag, but the example commands themselves explain both check + set. As there is only a single letter between enabled (check) and enable (set) this can be confusing if you only take a short look. This MR resolves this issue and explicitly states that the example describes a check and a set command.

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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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