Update 2D/3D button toggle images in Labels tutorial

[TimMonko]

🧰 Task

Update the button images found here: https://napari.org/stable/howtos/layers/labels.html#d-rendering
May also be in other howto tutorials, didn't check.

[psobolewskiPhD]

In case anyone is confused like me, the current 3D version is showing where the text says 2D and the old 3D version is showing where it says 3D.

[TimMonko]

Thanks Peter! I definitely made this post quick while in the middle of listening to a talk.
We may also want to consider that the new button image is much larger than previously. Maybe we normalize the size, but this is most likely going to be moot once we move to autogenerated images and thus control size programmatically