Bump tornado from 6.5.5 to 6.5.6

Bumps [tornado](https://github.com/tornadoweb/tornado) from 6.5.5 to 6.5.6.
- [Changelog](https://github.com/tornadoweb/tornado/blob/master/docs/releases.rst)
- [Commits](tornadoweb/tornado@v6.5.5...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]

requirements-notebook.txt

@@ -91,7 +91,7 @@ soupsieve==2.8.3
 stack-data==0.6.3
 terminado==0.18.1
 tinycss2==1.4.0
-tornado==6.5.5
+tornado==6.5.6
 traitlets==5.15.0
 typing_extensions==4.15.0
 tzdata==2026.2