Check for sRGB on Normal and Mask samplers instead checks against Greyscale and Alpha samplers

In FMaterialInstanceEditor::RefreshOnScreenMessages, there is a check for sRGB on Normal and Mask samplers.

The issue is the check uses a TextureCompressionSettings enum cast to EMaterialSamplerType rather than EMaterialSamplerType directly. The TextureCompressionSettings enum does not share indices with EMaterialSamplerType, so the TC_NormalMap becomes SAMPLERTYPE_Grayscale.

Seemingly, the correct check would be

if (Expression && ((Expression->SamplerType == SAMPLERTYPE_Normal || Expression->SamplerType == SAMPLERTYPE_Masks) && Texture->SRGB)).

Notably, this does not check virtual samplers, though.