Fix serialize migration

Skip validation on the serialize migration. This might sound scary, but we only have the data we have when the migration happens. Presumably if a validation would fail it's because there is a new property that a future migration will fix. 

Fixes #8157 
Fixes #8141
Fixes #8184 
@dblessing maybe its better to use just `save` instead of skipping validation. It will cause future problems when you expect field not nil but it is and so