Bump twig/markdown-extra from 3.19.0 to 3.20.0 in /web/landing

Bumps [twig/markdown-extra](https://github.com/twigphp/markdown-extra) from 3.19.0 to 3.20.0.
- [Commits](twigphp/markdown-extra@v3.19.0...v3.20.0)

---
updated-dependencies:
- dependency-name: twig/markdown-extra
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>