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

[DuskyElf]

Fixed .to_edge()'s example demonstration in docs

Added the missing object (c: Circle) in the scene demonstrating .to_edge(RIGHT) here -

Motivation and Explanation:

The example on To Edge Example demonstrated the use of .to_edge() method with three objects, two of them were added (in #3408) to the scene but one was missed. I was just reading through the docs, and was confused for a second looking for the missing circle.

Links to added or changed documentation pages

https://manimce--3958.org.readthedocs.build/en/3958/reference/manim.mobject.mobject.Mobject.html#toedgeexample But this link doesn't seem to work

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested

[behackl]

Well spotted, thanks for fixing this!

I'll merge this as soon as our docs build properly again.