Sculpt: Fix T104040: Always update eevee shadows in sculpt modes

source/blender/draw/engines/eevee/eevee_materials.c

@@ -848,6 +848,8 @@ void EEVEE_materials_cache_populate(EEVEE_Data *vedata,
 
         MATCACHE_AS_ARRAY(matcache, shadow_grp, materials_len, shgrps_array);
         DRW_shgroup_call_sculpt_with_materials(shgrps_array, gpumat_array, materials_len, ob);
+
+        *cast_shadow = true;
       }
       else {
         struct GPUMaterial **gpumat_array = BLI_array_alloca(gpumat_array, materials_len);

source/blender/draw/engines/eevee/eevee_shadows.c

@@ -139,6 +139,10 @@ void EEVEE_shadows_caster_register(EEVEE_ViewLayerData *sldata, Object *ob)
       BLI_BITMAP_SET(backbuffer->update, past_id, oedata->need_update);
     }
     update = oedata->need_update;
+
+    /* Always update shadow buffers in sculpt modes. */
+    update |= ob->sculpt != NULL;
+
     oedata->need_update = false;
   }