[RUN AS-IF-FOSS] Update gitlab-styles to 5.1.0

What does this MR do?

• Updates gitlab-styles to 5.1.0
• Removes LineBreakAroundConditionalBlock local in favor of upstreamed version in gitlab-styles
• Fixes empty line issue with let_it_be provided with gitlab-styles update. Note, this linting rule was already agreed upon with !36742 (merged), but had to disable again when adding in the fix for let_it_be. This re-enables it after fixing the exceptions.

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

Related to #277422, #263244