build(deps): bump actix-web in /atcoder-problems-backend

Bumps [actix-web](https://github.com/actix/actix-web) from 4.0.0-rc.2 to 4.0.1.
- [Release notes](https://github.com/actix/actix-web/releases)
- [Changelog](https://github.com/actix/actix-web/blob/master/CHANGES.md)
- [Commits](actix/actix-web@web-v4.0.0-rc.2...web-v4.0.1)

---
updated-dependencies:
- dependency-name: actix-web
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]