Fix apt_add fails on apt-key not found even if it is present

See merge request xebis/shellib!25

## [0.11.1](https://gitlab.com/xebis/shellib/compare/v0.11.0...v0.11.1) (2022-01-08)

### Bug Fixes

* apt_add fails on apt-key not found even if it is present ([a1fcfa22](https://gitlab.com/xebis/shellib/commit/a1fcfa22766ae16b0a7b1b5b39c746f3a96444c3))