chore(deps): bump regex from 2026.2.19 to 2026.2.28 in /hack/api-docs (#6012)

Bumps [regex](https://github.com/mrabarnett/mrab-regex) from 2026.2.19 to 2026.2.28.
- [Changelog](https://github.com/mrabarnett/mrab-regex/blob/hg/changelog.txt)
- [Commits](https://github.com/mrabarnett/mrab-regex/compare/2026.2.19...2026.2.28)

---
updated-dependencies:
- dependency-name: regex
  dependency-version: 2026.2.28
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

hack/api-docs/requirements.txt

@@ -31,7 +31,7 @@ pymdown-extensions==10.21
 python-dateutil==2.9.0.post0
 PyYAML==6.0.3
 pyyaml_env_tag==1.1
-regex==2026.2.19
+regex==2026.2.28
 requests==2.32.5
 six==1.17.0
 termcolor==3.3.0