GitLab

Backport #17242

It is possible that a keyring can contain duplicate keys on a keyring due to jpegs or
other layers. This currently leads to a confusing error for the user - where we report
a duplicate key insertion.

This PR simply coalesces keys into one key if there are duplicates.
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: 6543 <6543@obermui.de>