Doing-cli

What's Changed
* Update CI to run on python 3.9, drop 3.6 by timvink in https://github.com/ing-bank/doing-cli/pull/97
* Drop explicit support for python 3.6 as it is end of life by timvink in https://github.com/ing-bank/doing-cli/pull/98


**Full Changelog**: https://github.com/ing-bank/doing-cli/compare/v1.2.14...v1.2.15

Fixed

- The iteration must be parsed into a URL so that you can use `doing open sprint` 93

Added

- Add output_format parameter to `doing list` (88). It allows you to output a list of issues instead of the normal output.
- Add a guide on how to on bulk edit work items (90)
- Improve the handling of story points (89)
- Add story points filter in `doing list` (87)
- Provide clearer error message when trying to close an issue without story points (86)

Thank you, timvink 🎉

Fixed

- `doing init` creates duplicate keys (82). PR by operte

Added

- New `doing pr open` command, which is an alias for `doing open pr` (83) Thanks operte for the contribution 🎉

Fixed

- `doing issue list` and `doing open issues` now list all open issues as issues that are NOT closed. Previously we missed certain (custom) states like `Design` and `Ready`. (78). Thanks MHeus 🎉