stubgen: treat dlls as c modules (#14503)

Fixes #14028

Author: hauntsaninja

mypy/moduleinspect.py

@@ -36,7 +36,7 @@ def is_c_module(module: ModuleType) -> bool:
         # Could be a namespace package. These must be handled through
         # introspection, since there is no source file.
         return True
-    return os.path.splitext(module.__dict__["__file__"])[-1] in [".so", ".pyd"]
+    return os.path.splitext(module.__dict__["__file__"])[-1] in [".so", ".pyd", ".dll"]
 
 
 class InspectError(Exception):