Bump idna from 3.6 to 3.7 in /doc (#582)

Bumps [idna](https://github.com/kjd/idna) from 3.6 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v3.6...v3.7)

---
updated-dependencies:
- dependency-name: idna
  dependency-type: indirect
...

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

doc/requirements.txt

@@ -20,7 +20,7 @@ docutils==0.20.1
     #   myst-parser
     #   sphinx
     #   sphinx-rtd-theme
-idna==3.6
+idna==3.7
     # via requests
 imagesize==1.4.1
     # via sphinx