WIP: Lint MR title instead of commits when squash is enabled

What does this MR do?

When MRs are set to be squashed, Danger will lint the MR's title instead of the commit messages, which should prevent unnecessary failures on some MRs that contain bad commits but have Squash commits when merge request is accepted enabled.

Screenshots

This MR's title was linted instead of the commits

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