Update pygments requirement in the optional group (#9953)

Updates the requirements on [pygments](https://github.com/pygments/pygments) to permit the latest version.

Updates `pygments` to 2.20.0
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.17.0...2.20.0)

---
updated-dependencies:
- dependency-name: pygments
  dependency-version: 2.20.0
  dependency-type: direct:development
  dependency-group: optional
...

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

Author: dependabot[bot]

pyproject.toml

@@ -69,7 +69,7 @@ optional = [
   "legacy-cgi; python_version>='3.13'",
   "markdown>=3.3.7",
   "psycopg[binary]>=3.1.8",
-  "pygments>=2.17,<2.20",
+  "pygments>=2.17,<2.21",
   "pyyaml>=5.3.1,<6.1",
   "requests",
   "uritemplate",