bug: no update on child values

I found a bug on gormVersion=6.1.7.RELEASE
I updated it from 6.1.5.RELEASE where it also happened

example code:
```
Product.withTransaction {
Pro2t domainObject= Pro2t .get(id)
//domainObject.internal= "something1" // this level updates are ok
domainObject.child.interna2 = "something2" // second level does not triguer update
domainObject.save(flush: true, validate: false)
}
```

Start by reproducing the provided Product.withTransaction example with Pro2t.get(id), the nested child.interna2 assignment, and domainObject.save(flush: true, validate: false). Trace the save behavior for the second-level child value and compare it with the direct internal assignment. Done means the nested child change is persisted after the transaction.

Written by the indexing model from the issue text.