Resolve "Label picker: Line break on long label titles"

What does this MR do?

It fixes a case when selecting a label that's one long word without spaces, the label is breaking and showing below the label color span.

The update is applying flexbox and word-break to .label-item item.

I tried to keep the changes limited to solve the bug reported in #48771 (closed), but I'm not 100% sure it's not affecting any other areas.

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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 #48771 (closed)