Fix VSE thumbnails are displayed from incorrect scene

Add scene to rendering context, so it can be used for cache hashing.

source/blender/editors/space_sequencer/sequencer_thumbnails.c

@@ -187,6 +187,7 @@ static SeqRenderData sequencer_thumbnail_context_init(const bContext *C)
   SEQ_render_new_render_data(bmain, depsgraph, scene, 0, 0, sseq->render_size, false, &context);
   context.view_id = BKE_scene_multiview_view_id_get(&scene->r, STEREO_LEFT_NAME);
   context.use_proxies = false;
+  context.scene = scene;
 
   return context;
 }