Bump idna from 3.11 to 3.15 in /docs/sphinx (#6280)

Bumps [idna](https://github.com/kjd/idna) from 3.11 to 3.15.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.md)
- [Commits](https://github.com/kjd/idna/compare/v3.11...v3.15)

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

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

docs/sphinx/requirements.txt

@@ -64,7 +64,7 @@ gitpython==3.1.50
     # via rocm-docs-core
 greenlet==3.3.0
     # via sqlalchemy
-idna==3.11
+idna==3.15
     # via requests
 imagesize==1.4.1
     # via sphinx