Textures on Sprite3D nodes with animated region_rects wobble (new in 3.2.3, 3.2.2 was unaffected)

[tcoxon]

Godot version: 3.2.3-stable
Also tested on 3.2.2-stable and couldn't reproduce it.

OS/device including version:
Ubuntu Linux 16.04, 64-bit
GeForce GTX 970 with NVIDIA 384.130 driver
GLES3 backend

Issue description:
After upgrading to 3.2.3 we noticed some of the sprites in our project wobbling. I've attached an example as a reproducer. These are Sprite3D nodes with animated region_rects, but the wobbling may occur in other situations; I'm not certain.

In 3.2.2, notice the skull at the bottom of the Sprite is rock steady:

In 3.2.3 the skull appears to wobble side-to-side by fractions of a texture pixel:

(Apologies for the low-quality gifs.)

Steps to reproduce:

1. Open the reproduction project below in the Godot editor.
2. Select the AnimationPlayer node and preview an animation--idle and alt_idle demonstrate it most clearly.

Minimal reproduction project:
wobbly_sprites.zip

[akien-mga]

Fixed by #42537.