Bump tornado from 6.5.1 to 6.5.6 in /docs

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.5.1 to 6.5.6.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.5.1...v6.5.6)

---
updated-dependencies:
- dependency-name: tornado
  dependency-version: 6.5.6
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -8,7 +8,7 @@ pylsl==1.16.1
 PyYAML==6.0.1
 PyYAML==6.0.1
 scipy==1.11.1
-tornado==6.5.1
+tornado==6.5.6
 sentry_sdk==2.8.0
 sphinx-rtd-theme==1.3.0
 sphinx==7.2.4