build(deps): bump github.com/spf13/cobra from 1.8.1 to 1.9.1

Bumps [github.com/spf13/cobra](https://github.com/spf13/cobra) from 1.8.1 to 1.9.1.
- [Release notes](https://github.com/spf13/cobra/releases)
- [Commits](spf13/cobra@v1.8.1...v1.9.1)

---
updated-dependencies:
- dependency-name: github.com/spf13/cobra
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Remove CircleCI

CircleCI tests currently seem fail consistently. GitHub actions
introduced in #136 are providing the same coverage (and more), have been
running stable for over a year and are easier to maintain. Thus, remove
Circle CI integration.

Ref. #136 (comment)