http://bbergeron.i2p/posts/2024-11-14_how-to-merge-divergent-git-histories.html
To fix this,
offer every developer who made a signed commit in that repository the
chance to sign their commits again with the following command. This
workaround is far from bulletproof. First, it’s slow, impractical and
annoying; secondly, it could potentially make developers sign commits
they didn’t initially sign (including potentially “forged” commits).