Update dependency async to v2.6.4

[mend-for-github-com[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
async (source)	2.6.1 -> 2.6.4

---

Release Notes

caolan/async (async)

### [`v2.6.4`](https://togithub.com/caolan/async/compare/v2.6.3...v2.6.4) [Compare Source](https://togithub.com/caolan/async/compare/v2.6.3...v2.6.4) ### [`v2.6.3`](https://togithub.com/caolan/async/compare/v2.6.2...v2.6.3) [Compare Source](https://togithub.com/caolan/async/compare/v2.6.2...v2.6.3) ### [`v2.6.2`](https://togithub.com/caolan/async/compare/v2.6.1...v2.6.2) [Compare Source](https://togithub.com/caolan/async/compare/v2.6.1...v2.6.2)

---

Configuration

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

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ 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