Subclass schema mapping with tablePerHierarchy false

When using tablePerHierarchy false, i lost subclass schema mapping and consequently, get this error:

`Caused by: org.postgresql.util.PSQLException: ERROR: relation "school_year_regular" does not exist`

```
class SchoolYear {
...
static mapping = {
table schema: 'agis'
discriminator column: "type"
tablePerHierarchy false
}
}
```

```
class SchoolYearRegular extends SchoolYear {
...
static mapping = {
table schema: 'agis'
discriminator "Regular"
}
}
```

### Environment Information
grailsVersion=4.0.8
gormVersion=7.0.4
gradleWrapperVersion=5.6.4

Start by reproducing the SchoolYear and SchoolYearRegular mappings with tablePerHierarchy false on the stated Grails, GORM, Gradle, and PostgreSQL versions. Investigate how the subclass table schema is resolved; done means the subclass query uses the agis schema and no longer reports that school_year_regular does not exist.

Written by the indexing model from the issue text.