Fix return value for float-version of `mix()` in shading reference (#3812)

tutorials/shading/shading_reference/shading_language.rst

@@ -753,7 +753,7 @@ When vec_type (float), vec_int_type, vec_uint_type, vec_bool_type nomenclature i
 +------------------------------------------------------------------------+---------------------------------------------------------------+
 | vec_type **clamp** (vec_type x, vec_type min, vec_type max)            | Clamp to ``min..max``                                         |
 +------------------------------------------------------------------------+---------------------------------------------------------------+
-| vec_type **mix** (float a, float b, float c)                           | Linear interpolate                                            |
+| float **mix** (float a, float b, float c)                              | Linear interpolate                                            |
 +------------------------------------------------------------------------+---------------------------------------------------------------+
 | vec_type **mix** (vec_type a, vec_type b, float c)                     | Linear interpolate (scalar coefficient)                       |
 +------------------------------------------------------------------------+---------------------------------------------------------------+