Fix: .to_edge()'s example demonstration in docs (#3958)

* ToEdgeExample's circle is added to the scene

* Made it consistent to the surrounding code

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Co-authored-by: Aarush Deshpande <110117391+JasonGrace2282@users.noreply.github.com>

manim/mobject/mobject.py

@@ -1498,7 +1498,7 @@ def construct(self):
                     tex_top.to_edge(UP)
                     tex_side = Tex("I am moving to the side!")
                     c = Circle().shift(2*DOWN)
-                    self.add(tex_top, tex_side)
+                    self.add(tex_top, tex_side, c)
                     tex_side.to_edge(LEFT)
                     c.to_edge(RIGHT, buff=0)