fix(richtext-lexical): Link: serialize newTab to target="_blank"

[linobino1]

Issue https://github.com/payloadcms/payload/issues/5256 re-appeared in Payload v.3.x-beta, this PR fixes it again.

Type of Change:

• [ ] Chore (non-breaking change which does not add functionality)
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Change to the templates directory (does not affect core functionality)
• [ ] Change to the examples directory (does not affect core functionality)
• [ ] This change requires a documentation update

Checklist:

• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] Existing test suite passes locally with my changes
• [ ] I have made corresponding changes to the documentation