Bump idna from 3.10 to 3.15 in /requirements/docs

Bumps [idna](https://github.com/kjd/idna) from 3.10 to 3.15.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.md)
- [Commits](kjd/idna@v3.10...v3.15)

---
updated-dependencies:
- dependency-name: idna
  dependency-version: '3.15'
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements/docs/requirements.txt

@@ -4,7 +4,7 @@ certifi==2025.7.9 ; python_version >= "3.9"
 charset-normalizer==3.4.2 ; python_version >= "3.9"
 colorama==0.4.6 ; python_version >= "3.9" and sys_platform == "win32"
 docutils==0.21.2 ; python_version >= "3.9"
-idna==3.10 ; python_version >= "3.9"
+idna==3.15 ; python_version >= "3.9"
 imagesize==1.4.1 ; python_version >= "3.9"
 importlib-metadata==8.7.0 ; python_version == "3.9"
 jinja2==3.1.6 ; python_version >= "3.9"