Ignore error about incompatible override in RowProxy (#230)

The signature of `Mapping.items` was changed in typeshed. I'm not
sure whether sqlalchemy conforms strictly to the new signature, so
I'm keeping the current signature and silencing the error.

Author: JukkaL

sqlalchemy-stubs/engine/result.pyi

@@ -29,7 +29,7 @@ class RowProxy(BaseRowProxy):
     def __eq__(self, other): ...
     def __ne__(self, other): ...
     def has_key(self, key): ...
-    def items(self) -> _RowItems: ...
+    def items(self) -> _RowItems: ...  # type: ignore[override]
     def keys(self): ...
     def iterkeys(self): ...
     def itervalues(self): ...