chore: pygments>=2.20.0 across all packages (CVE-2026-4539) (#36385)

## Summary

Bumps `pygments` to `>=2.20.0` across all 21 affected packages to
address [CVE-2026-4539](https://github.com/advisories/GHSA-XXXX) — ReDoS
via inefficient GUID regex in Pygments.

- **Severity:** Low
- **Fixed in:** 2.20.0 (was 2.19.2)
- **Change:** Added `pygments>=2.20.0` to `constraint-dependencies` in
`[tool.uv]` for each package, then ran `uv lock --upgrade-package
pygments` to regenerate lock files.

Closes Dependabot alerts #3435–#3455.

## Release Note
Patch deps

### Test Plan
 - [x] CI Green 🙏

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

libs/standard-tests/pyproject.toml

@@ -62,7 +62,7 @@ typing = [
 langchain-core = { path = "../core", editable = true }
 
 [tool.uv]
-constraint-dependencies = ["urllib3>=2.6.3"]
+constraint-dependencies = ["urllib3>=2.6.3", "pygments>=2.20.0"]
 
 [tool.mypy]
 plugins = ["pydantic.mypy"]