chore(deps): bump regex from 2025.8.29 to 2025.9.1 in /hack/api-docs (#5282)

Bumps [regex](https://github.com/mrabarnett/mrab-regex) from 2025.8.29 to 2025.9.1.
- [Changelog](https://github.com/mrabarnett/mrab-regex/blob/hg/changelog.txt)
- [Commits](https://github.com/mrabarnett/mrab-regex/compare/2025.8.29...2025.9.1)

---
updated-dependencies:
- dependency-name: regex
  dependency-version: 2025.9.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

hack/api-docs/requirements.txt

@@ -31,7 +31,7 @@ pymdown-extensions==10.16.1
 python-dateutil==2.9.0.post0
 PyYAML==6.0.2
 pyyaml_env_tag==1.1
-regex==2025.8.29
+regex==2025.9.1
 requests==2.32.5
 six==1.17.0
 termcolor==3.1.0