chore(deps): bump tornado in /helm-chart/images/binderhub

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.4.1 to 6.4.2.
- [Changelog](https://github.com/tornadoweb/tornado/blob/v6.4.2/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.4.1...v6.4.2)

---
updated-dependencies:
- dependency-name: tornado
  dependency-type: direct:production
...

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

helm-chart/images/binderhub/requirements.txt

@@ -178,7 +178,7 @@ sqlalchemy==2.0.31
     # via
     #   alembic
     #   jupyterhub
-tornado==6.4.1
+tornado==6.4.2
     # via
     #   -r ../../../requirements.txt
     #   jupyterhub