Add tests about matching __slots__ against structural type (PY-29233)

python/testData/inspections/PyTypeCheckerInspection/PassClassWithDunderSlotsToMethodThatUsesSlottedAttribute.py

@@ -2,8 +2,29 @@ class A(object):
     __slots__ = 'x', 'y'
 
 
+class B(object):
+    __slots__ = ['x']
+
+class C(B):
+    pass
+
+
+class D(object):
+    pass
+
+class E(D):
+    __slots__ = ['x']
+
+
+class F:
+    __slots__ = ['x']
+
+
 def copy_values(a):
     print(a.x)
 
 
-copy_values(A())
+copy_values(A())
+copy_values(C())
+copy_values(E())
+copy_values(<warning descr="Type 'D' doesn't have expected attribute 'x'">D()</warning>)