If you are talking about the window itself, I'm not aware of ways to do so in Godot (never saw Windows applications resizing like that). At worse you could place a check in
_process which forcefully sets
OS.window_size to the closest valid size?
However, you could use another stretch aspect option to keep the aspect ratio (and allow players to play fullscreen if they don't own a screen of the same ratio as your game), but due to the above it will always cause black bars to appear.
See here for more info: https://docs.godotengine.org/en/3.0/tutorials/viewports/multiple_resolutions.html