Conflicting information about PNG transparency support in "Creating movies" tutorial and "MovieWriter" documentation.

**Your Godot version:**
4.2

**Issue description:**
There is conflicting information about PNG transparency support in the "Creating movies" tutorial and the MovieWriter class documentation. The tutorial says it is supported, and the class documentation says it isn't. I tried following the tutorial's instructions and didn't get transparent PNGs out of it, but it's possible I did something wrong.

Creating movies
MovieWriter

**URL to the documentation page:**
https://docs.godotengine.org/en/stable/classes/class_moviewriter.html
https://docs.godotengine.org/en/stable/tutorials/animation/creating_movies.html