Ellipse preserves width and height when animating (behaves like circle)

Nobody has claimed this yet.

## Description of bug / unexpected behavior

```py
class CircleStretch(Scene):
def construct(self):
ellipse = Ellipse(width=1, height=2)
self.wait()
self.play(ellipse.animate.set(width=6))
self.wait()
```

This code results in the following animation where the [`Ellipse`](https://docs.manim.community/en/stable/reference/manim.mobject.geometry.Ellipse.html?highlight=ellipse), inheriting from [`Circle`](https://docs.manim.community/en/stable/reference/manim.mobject.geometry.Circle.html#manim.mobject.geometry.Circle), preserves the ratio of its half-axes. We get the same output when explicitly specifying the height:

```py
self.play(ellipse.animate.set(width=6).set(height=2))
```

https://user-images.githubusercontent.com/37160523/152845603-4c7c8e04-dccf-4e5f-9aa6-805d42b1fe56.mp4

## Expected behavior
What I expected is that only the width changes, while the height stays the same. This is why I'm using the `Ellipse` instead of the `Circle` in the first place. The expected output can be achieved using this code:

```py
class CircleStretch(Scene):
def construct(self):
ellipse = Ellipse(width=1, height=2)
self.add(ellipse)
self.wait()
self.play(ellipse.animate.stretch_to_fit_width(6))
self.wait()
```

While this works fine, it's just a bit irritating that the other way doesn't work.

https://user-images.githubusercontent.com/37160523/152845838-d084d7b3-7e8a-419d-b171-57247f3d1ba3.mp4

## System specifications

System Details

- OS: Windows 10 Version 21H1
- RAM: 16 GB
- Python version: 3.9.7
- Installed modules (provide output from `pip list`):
```
Package Version
------------------- -----------
atomicwrites 1.4.0
attrs 21.2.0
autopep8 1.5.7
backcall 0.2.0
beautifulsoup4 4.10.0
certifi 2021.5.30
charset-normalizer 2.0.4
click 8.0.3
click-default-group 1.2.2
cloup 0.7.1
colorama 0.4.4
colour 0.1.5
commonmark 0.9.1
cycler 0.10.0
debugpy 1.4.1
decorator 5.1.1
dimod 0.10.7
dwave-networkx 0.8.10
dwave-preprocessing 0.3.1.post0
et-xmlfile 1.1.0
glcontext 2.3.4
idna 3.2
iniconfig 1.1.1
ipykernel 6.2.0
ipython 7.26.0
ipython-genutils 0.2.0
isosurfaces 0.1.0
jedi 0.18.0
jupyter-client 6.1.12
jupyter-core 4.7.1
kiwisolver 1.3.1
manim 0.14.0
ManimPango 0.4.0.post2
mapbox-earcut 0.12.11
matplotlib 3.4.3
matplotlib-inline 0.1.2
moderngl 5.6.4
moderngl-window 2.4.1
multipledispatch 0.6.0
networkx 2.6.3
numpy 1.19.3
openpyxl 3.0.8
packaging 21.0
pandas 1.3.2
parso 0.8.2
pickleshare 0.7.5
Pillow 8.0.1
pip 22.0.3
pluggy 1.0.0
prompt-toolkit 3.0.19
py 1.10.0
pycairo 1.20.1
pycodestyle 2.7.0
pydub 0.25.1
pyglet 1.5.21
Pygments 2.10.0
pyparsing 2.4.7
pyrr 0.10.3
pytest 6.2.5
python-dateutil 2.8.1
pytz 2021.1
pywin32 301
pyzmq 22.2.1
requests 2.26.0
rich 11.1.0
scipy 1.8.0
screeninfo 0.6.7
setuptools 57.4.0
six 1.15.0
skia-pathops 0.7.2
soupsieve 2.2.1
srt 3.5.1
toml 0.10.2
tornado 6.1
tqdm 4.62.3
traitlets 5.0.5
urllib3 1.26.6
watchdog 2.1.6
wcwidth 0.2.5
XlsxWriter 3.0.1
```

LaTeX details

+ LaTeX distribution: using MiKTeX Console 4.6
+ Installed LaTeX packages:
probably not needed for this issue (packages list is huge for MikTeX, one single screenshot won't suffice)

FFMPEG

Output of `ffmpeg -version`:

```
4.2.3
```

## Additional comments

Start from the Ellipse and Circle entry points and reproduce the reported animation using set(width=6), then compare it with stretch_to_fit_width(6). Trace how width and height are handled during animation, and consider the issue resolved when changing only the width preserves the ellipse's height without changing its axis ratio.

Written by the indexing model from the issue text.