gh-122988: Clarify that types.get_original_bases() ignores inherited __orig_bases__ - #156917

The docs for types.get_original_bases() say that for classes that have an __orig_bases__ attribute, the function returns cls.__orig_bases__. That reads as if the function is equivalent to attribute access, but the implementation only looks in cls.__dict__. A class whose base defines __orig_bases__ will inherit the attribute, while get_original_bases() correctly falls back to cls.__bases__ for it.

This rewords the paragraph to say the lookup is on the class's own namespace and that inherited attributes are ignored, and adds a short example of that case to the existing examples block.

Fixes #122988

• Issue: get_original_bases does not return what cls.__orig_bases__ returns #122988