Bump demisto-sdk from 1.15.5 to 1.20.5 in /docker/demisto-sdk

Bumps [demisto-sdk](https://github.com/demisto/demisto-sdk) from 1.15.5 to 1.20.5.
- [Release notes](https://github.com/demisto/demisto-sdk/releases)
- [Changelog](https://github.com/demisto/demisto-sdk/blob/master/CHANGELOG.md)
- [Commits](demisto/demisto-sdk@v1.15.5...v1.20.5)

---
updated-dependencies:
- dependency-name: demisto-sdk
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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