Add missing `keyring` dep in setup.py and pyproject.toml

[tucksaun]

This PR

Add missing keyring dep in setup.py and pyproject.toml.

• [X] I've read the DCO.
• [X] I've read the Coding Guidelines
• [X] The relevant informations about the changes stands in the commit message, not here in the message of the pull request.
• [X] Code changes follow the style of the files they change.
• [X] Code is tested (pip install --no-cache-dir -v git+https://github.com/tucksaun/offlineimap3.git@master works successfully + GHA).

References

Additional information

#102 added support of system keyring and added keyring to requirements.txtbut not insetup.pynorpyproject.toml. As a result the installation of offlineimap using pip pip install --no-cache-dir -v git+https://github.com/OfflineIMAP/offlineimap3.git@master` does not work anymore. Adding the missing dependency to those files fixes it.