collection collection: fix swapped keys and values return types. (#67)

Author: MaicoTimmerman

sqlalchemy-stubs/sql/base.pyi

@@ -149,8 +149,8 @@ class ColumnCollection(Generic[_CE]):
     def __init__(
         self, columns: Optional[Iterable[Tuple[str, _CE]]] = ...
     ) -> None: ...
-    def keys(self) -> List[_CE]: ...
-    def values(self) -> List[str]: ...
+    def keys(self) -> List[str]: ...
+    def values(self) -> List[_CE]: ...
     def items(self) -> List[Tuple[str, _CE]]: ...
     def __bool__(self) -> bool: ...
     def __len__(self) -> int: ...