Added test for correct nested class name in inheritance diagram

tests/roots/test-inheritance/diagram_w_nested_classes.rst

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+Diagram with Nested Classes
+===========================
+
+.. inheritance-diagram::
+    dummy.test_nested

tests/roots/test-inheritance/dummy/test_nested.py

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+r"""
+
+    Test with nested classes.
+
+"""
+
+
+class A(object):
+    class B(object):
+        pass
+
+
+class C(A.B):
+    pass