[luigi617]

Bumps Jinja2 3.0.3 → 3.1.6 for the docs build, fixing Dependabot alerts #43, #44, #45, #46, #47 (GHSA-h5c8-rqwp-cp95, GHSA-h75v-3vvj-5mfj, GHSA-q2x7-8rv6-6q7h, GHSA-gmj6-6f8f-6699, GHSA-cpwx-vrp4-4pq7).

• requirements-docs.txt: Jinja2<3.1.0 → Jinja2==3.1.6 (exact pin, matching Sphinx==6.2). The cap came from e4e4fbd ("Jinja2 3.1.0 breaks our doc build process") back when the docs used an older Sphinx. Sphinx 6.2 supports Jinja2 3.1, and the docs code (including the vendored guzzle_sphinx_theme) doesn't use any of the APIs removed in 3.1.
• The lock file was regenerated with pip-compile on Python 3.9 using the command in its header, with --upgrade-package so only this package changes.

Testing (end-to-end)

Built the full HTML docs (make html, Python 3.9, Sphinx 6.2.0) on both v2 (Jinja2 3.0.3, Pygments 2.19.2) and this branch (Jinja2 3.1.6), then compared the two output trees with diff -rq:

• Both builds produced 61,660 files, and every page matches byte for byte. The only file that differs is .buildinfo, where the config: hash changes because html_theme_path in conf.py is an absolute path and each build ran from a different checkout.
• Both builds logged the same 1,482 warnings. These are existing RST warnings in the generated service reference pages.
• Jinja2 ran across the whole site, because every page is rendered through the guzzle_sphinx_theme Jinja templates.

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This PR was generated by AI tools, and reviewed by @luigi617.