A bug in 0.21.x and 22.x resulted in some wallets having invalid derivation paths that are the concatenation of two derivation paths. These appear only when inactive hd chains are topped up.
Since key metadata is a legacy wallet only record, migrating legacy wallets to descriptor wallets will fix this issue as all key metadata records are deleted. The derivation path information is derived on-the-fly from the descriptor that is produced for the inactive hd chain.
Thus we only need a test to verify that the derivation paths are good, and that all key metadata records are deleted from the migrated wallet.