Scene size does not match viewer

I was redoing some 3d scenes and I came across a (potential) bug.

The problem I'm having is that if I change the size of a figure, the viewer changes size, but not the scene.

The following two code snippets produce the images
```Python
from mayavi.core.ui.mayavi_scene import MayaviViewer
viewer = MayaviViewer()
viewer.menu_bar_manager = None
viewer.size = (800, 800)
viewer.open()
```

```Python
from mayavi.core.ui.mayavi_scene import MayaviViewer
viewer = MayaviViewer()
viewer.menu_bar_manager = None
viewer.size = (1024, 1024)
viewer.open()
```

But, If I play with a scene, I can change the size and I have no issues.
```
from mayavi.core.ui.mayavi_scene import MayaviScene
from mayavi.preferences.api import set_scene_preferences, \
get_scene_preferences
p = get_scene_preferences()
s = MayaviScene(None, stereo=p['stereo'])
set_scene_preferences(s, p)
s.show(True)
```

The problem is that `viewer.size = (1024, 1024)` changes the size of the window but not the scene, `viewer.scene.set_size((1024, 1024))` has no effect and `s.set_size((1024, 1024))` works fine.

Here's some of the relevant packages versions. I'm using Mayavi dev and MacOS 10.15.3. I had the same issue before updating, using python 3.6/3.7.
```
pyface 6.1.2 py38_0
pyqt 5.9.2 py38h655552a_2
python 3.8.1 h359304d_1
traits 5.2.0 py38h1de35cc_0
traitsui 6.1.3 py_0
vtk 8.2.0 py38hb651df3_207 conda-forge
```

Any clue on fixing this issue? the problem is that I need high resolution scenes to save them to a PNG, but I can't change the resolution in a figure (`mayavi.core.scene.Scene`).