build(deps): bump idna from 3.7 to 3.15 in /requirements

Bumps [idna](https://github.com/kjd/idna) from 3.7 to 3.15.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.md)
- [Commits](kjd/idna@v3.7...v3.15)

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

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

Author: dependabot[bot]

requirements/checkdocs.txt

@@ -23,7 +23,7 @@ docutils==0.17.1
     #   myst-parser
     #   sphinx
     #   sphinx-rtd-theme
-idna==3.7
+idna==3.15
     # via requests
 imagesize==1.4.1
     # via sphinx

requirements/docs.txt

@@ -23,7 +23,7 @@ docutils==0.17.1
     #   myst-parser
     #   sphinx
     #   sphinx-rtd-theme
-idna==3.7
+idna==3.15
     # via requests
 imagesize==1.4.1
     # via sphinx