TST: create tests to check if docs are rendering correctly

[Gui-FernandesBR]

Describe the bug

When accessing the documentation of the Rocket.addTrapezoidalFins method. The docs that are built are not following the correct format.

To Reproduce

Just access the following link: (https://docs.rocketpy.org/en/latest/reference/classes/Rocket.html?highlight=addtrapezo#rocketpy.Rocket.Rocket.addTrapezoidalFins)

Expected behavior

Something like this whoud happen:

Screenshots

Additional context

This issue was reported by an user in our discord server. I'm saving here so we don't forget it!

[giovaniceotto]

May be useful to prevent future errors similar to this: https://stackoverflow.com/questions/33896196/how-to-test-the-validity-of-your-sphinx-documentation