fix: MeshTransmissionMaterial prevent setting values on discard mat when backside is off

[vis-prime]

Why

In drei/MeshtransmissionMaterial

in this section

drei/src/core/MeshTransmissionMaterial.tsx

Lines 416 to 436 in 9edcade

	parent.material = discardMaterial
	if (backside) {
	// Render into the backside buffer
	state.gl.setRenderTarget(fboBack)
	state.gl.render(state.scene, state.camera)
	// And now prepare the material for the main render using the backside buffer
	parent.material = ref.current
	parent.material.buffer = fboBack.texture
	parent.material.thickness = backsideThickness
	parent.material.side = THREE.BackSide
	}
	// Render into the main buffer
	state.gl.setRenderTarget(fboMain)
	state.gl.render(state.scene, state.camera)
	parent.material.thickness = thickness
	parent.material.side = side
	parent.material.buffer = fboMain.texture

if backside is off , mtm is not restored on the "parent" mesh

so in the next lines thickness, side, and buffer are actually being set on the discard material instead of mtm

What

Moving parent.material = ref.current before the value is set
This error does not affect r3f somehow

Checklist

• Documentation updated (example)
• Storybook entry added (example)
• Ready to be merged

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Name	Status	Preview	Comments	Updated (UTC)
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