Bump jinja2 from 2.8 to 3.1.3 in /doc (#89)

Bumps [jinja2](https://github.com/pallets/jinja) from 2.8 to 3.1.3.
- [Release notes](https://github.com/pallets/jinja/releases)
- [Changelog](https://github.com/pallets/jinja/blob/main/CHANGES.rst)
- [Commits](pallets/jinja@2.8...3.1.3)

---
updated-dependencies:
- dependency-name: jinja2
  dependency-type: direct:production
...

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

doc/requirements.txt

@@ -6,7 +6,7 @@ backports.ssl-match-hostname==3.5.0.1
 certifi==2022.12.7
 CommonMark==0.5.4
 docutils==0.12
-Jinja2==2.8
+Jinja2==3.1.3
 livereload==2.4.1
 MarkupSafe==0.23
 pathtools==0.1.2