More frequent `UpdateManifest failed` errors when pushing to DoltHub

With the database https://www.dolthub.com/repositories/holywritings/bahaidata on checkout 1rjkfjgdultskt2aafj3en2vpt861h3d I did an `ALTER TABLE pages MODIFY COLUMN comment VARCHAR(1000)`, which resulted in the error "unknown push error; rpc error: code = Internal desc = UpdateManifest failed".

Waiting a bit resulted in a successful push a bit later.

Reproduce the reported ALTER TABLE pages MODIFY COLUMN comment VARCHAR(1000) followed by a push on the Bahaidata checkout, and observe whether UpdateManifest failed recurs. Start from the push path and the UpdateManifest error entry point; done means the schema change can be pushed reliably without the intermittent RPC failure.

Written by the indexing model from the issue text.