Bump idna from 3.4 to 3.7 in /docs (#653)

Bumps [idna](https://github.com/kjd/idna) from 3.4 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v3.4...v3.7)

---
updated-dependencies:
- dependency-name: idna
  dependency-type: direct:production
...

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

docs/requirements.txt

@@ -9,7 +9,7 @@ charset-normalizer==3.2.0
 click==8.1.6
 colorama==0.4.6
 docutils==0.18.1
-idna==3.4
+idna==3.7
 imagesize==1.4.1
 jinja2==3.1.3
 livereload==2.6.3