Fix: EEVEE-Next: Principled BSDF transmission color applied twice

This was caused by the 2 transmission event approximation we
do for object with non-null thickness. This follows cycles
by using the square root of the color.

source/blender/gpu/shaders/material/gpu_shader_material_principled.glsl

@@ -167,7 +167,11 @@ void node_bsdf_principled(vec4 base_color,
     vec3 reflectance, transmittance;
     bsdf_lut(F0,
              F90,
+#ifdef GPU_SHADER_EEVEE_LEGACY_DEFINES
              clamped_base_color.rgb,
+#else
+             sqrt(clamped_base_color.rgb),
+#endif
              NV,
              roughness,
              ior,