Update dependency tornado to v6.4.1

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
tornado (source)	==6.4 -> ==6.4.1

---

Release Notes

tornadoweb/tornado (tornado)

### [`v6.4.1`](https://togithub.com/tornadoweb/tornado/compare/v6.4.0...v6.4.1) [Compare Source](https://togithub.com/tornadoweb/tornado/compare/v6.4.0...v6.4.1)

---

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by Mend Renovate. View repository job log here.