ViewportTextureNode: Change update type to RENDER.

[Mugen87]

Fixed #32642.

Description

As suggested in #32642 (comment), the PR changes the update type of ViewportTextureNode from FRAME to RENDER. This ensures viewport textures reflect the current state of the bound framebuffer when a render call happens which is not true when using FRAME.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	355.36 84.47	355.36 84.47	+0 B +0 B
WebGPU	621.33 172.52	621.34 172.52	+1 B +1 B
WebGPU Nodes	619.94 172.27	619.94 172.27	+1 B +1 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	487.23 119.23	487.23 119.23	+0 B +0 B
WebGPU	692.28 187.78	692.28 187.78	+0 B +2 B
WebGPU Nodes	642.08 175	642.08 175	+0 B +1 B