Bump jinja2 from 3.0.3 to 3.1.3 in /docs (OpenNMT#2551)

Bumps [jinja2](https://github.com/pallets/jinja) from 3.0.3 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@3.0.3...3.1.3)

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

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

docs/requirements.txt

@@ -1,6 +1,6 @@
 docutils==0.19
 sphinx==6.1.3
-Jinja2==3.0.3
+Jinja2==3.1.3
 sphinxcontrib.bibtex==2.5.0
 sphinxcontrib.mermaid==0.8.1
 sphinx-rtd-theme==0.4.3