WebGLRenderer: Correctly restore render target during transmission pass.

[Mugen87]

Fixed #31318.

Description

The transmission pass of WebGLRenderer does not correctly restore the render target state which produces a wrong output when rendering with a cube camera.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	337.65 78.76	337.71 78.77	+55 B +7 B
WebGPU	557.6 154.28	557.6 154.28	+0 B +0 B
WebGPU Nodes	556.52 154.07	556.52 154.07	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	468.89 113.45	468.94 113.46	+55 B +9 B
WebGPU	632.96 171.3	632.96 171.3	+0 B +0 B
WebGPU Nodes	588.01 160.61	588.01 160.61	+0 B +0 B