Add redefined-slots-in-subclass documentation examples (#6079)

Author: mbyrnepr2

doc/data/messages/r/redefined-slots-in-subclass/bad.py

@@ -0,0 +1,6 @@
+class Base:
+    __slots__ = ("a", "b")
+
+
+class Subclass(Base):
+    __slots__ = ("a", "d")  # [redefined-slots-in-subclass]

doc/data/messages/r/redefined-slots-in-subclass/good.py

@@ -0,0 +1,6 @@
+class Base:
+    __slots__ = ("a", "b")
+
+
+class Subclass(Base):
+    __slots__ = ("c", "d")