Fix T80080: improve tooltip for render number of threads

Since the switch to TBB, the threads value specificies the maximum number of
CPU cores used while rendering, it is not longer possible to use more threads
than cores. Change the tooltip to make this more clear.

source/blender/makesrna/intern/rna_scene.c

@@ -5935,7 +5935,7 @@ static void rna_def_scene_render_data(BlenderRNA *brna)
   RNA_def_property_int_funcs(prop, "rna_RenderSettings_threads_get", NULL, NULL);
   RNA_def_property_ui_text(prop,
                            "Threads",
-                           "Number of CPU threads to use simultaneously while rendering "
+                           "Maximum number of CPU cores to use simultaneously while rendering "
                            "(for multi-core/CPU systems)");
   RNA_def_property_update(prop, NC_SCENE | ND_RENDER_OPTIONS, NULL);