Sync KnownExecModelDifferenceTest with document migration section

Issue Description:

Now we have "Migration from non-executable model to executable model" section in docs.
https://docs.drools.org/latest/drools-docs/docs-website/drools/migration-guide/index.html#nonexec-model-to-exec-model_migration-guide

KnownExecModelDifferenceTest is to verify the known behavior differences, so review the section and unit tests. Add test cases if missing.

Acceptance Criteria:

KnownExecModelDifferenceTest test cases matches the "Migration from non-executable model to executable model" section explanation.

Particularly, DROOLS-7198 (Invalid cast) and DROOLS-7218 (Add a different type instance to generics List)