fix (test): SQLAlchemy type annotation error.

Type annotation can’t be interpreted for Annotated Declarative Table form.

https://docs.sqlalchemy.org/en/20/errors.html#type-annotation-can-t-be-interpreted-for-annotated-declarative-table-form
Signed-off-by: Paulo Vital <paulo.vital@ibm.com>

Author: pvital

tests/clients/test_sqlalchemy.py

@@ -22,6 +22,7 @@
 
 class StanUser(Base):
     __tablename__ = "churchofstan"
+    __allow_unmapped__ = True
 
     id = Column(Integer, primary_key=True)
     name = Column(String)