Fix typo in dataclasses.py (#16173)

```
heirarchy -> hierarchy
```

mypy/plugins/dataclasses.py

@@ -730,7 +730,7 @@ def _freeze(self, attributes: list[DataclassAttribute]) -> None:
         for attr in attributes:
             # Classes that directly specify a dataclass_transform metaclass must be neither frozen
             # non non-frozen per PEP681. Though it is surprising, this means that attributes from
-            # such a class must be writable even if the rest of the class heirarchy is frozen. This
+            # such a class must be writable even if the rest of the class hierarchy is frozen. This
             # matches the behavior of Pyright (the reference implementation).
             if attr.is_neither_frozen_nor_nonfrozen:
                 continue