build(deps-dev): bump rxjs from 7.3.1 to 7.4.0

Bumps [rxjs](https://github.com/reactivex/rxjs) from 7.3.1 to 7.4.0.
- [Release notes](https://github.com/reactivex/rxjs/releases)
- [Changelog](https://github.com/ReactiveX/rxjs/blob/master/CHANGELOG.md)
- [Commits](ReactiveX/rxjs@7.3.1...7.4.0)

---
updated-dependencies:
- dependency-name: rxjs
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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