Bump sixgill-clients from 0.2.25 to 0.2.26 in /docker/sixgill (#24673)

Bumps [sixgill-clients](https://bitbucket.org/sixgill/cybersixgill-client) from 0.2.25 to 0.2.26.
- [Commits](https://bitbucket.org/sixgill/cybersixgill-client/commits)

---
updated-dependencies:
- dependency-name: sixgill-clients
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>