Support pygments>=2.20.0 (CVE-2026-4539)

[nikolaysm]

Problem

pygments 2.20.0 was released to fix CVE-2026-4539.
However, mkdocs-techdocs-core currently pins pygments to a version range that excludes >=2.20.0,
preventing downstream projects from upgrading to the patched release.

Request

Please update the pygments dependency constraint in mkdocs-techdocs-core to allow >=2.20.0.

Impact

Projects using mkdocs-techdocs-core are unable to resolve the CVE-2026-4539 vulnerability
as long as this constraint is in place. pip-audit will continue to flag the vulnerability
with no available workaround.