[luigi617]

Bumps Pygments 2.19.2 → 2.20.0 in requirements-docs-lock.txt to fix Dependabot alert #49 (GHSA-5239-wwwm-4pmq, ReDoS in GUID matching).

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. Pygments 2.20.0 still supports Python 3.9.

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 (Pygments 2.20.0), 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.
• Pygments ran across the whole site: 20,031 pages contain syntax-highlighted code blocks, and _static/pygments.css is identical.

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