Fix T93194: greasepencil channel lists ignoring collection visibility

Same fix as rB0a3b4d4c64f1, but this time for greasepencil.

To repeat: dopesheet in greasepencil mode was ignoring the temporariy
visibility flag of collections. As a result, even though the dopesheet
was supposed to show animation data of visible greasepencils only was
still showing such data of greasepencils that were hidden by hiding
their collection.

source/blender/editors/animation/anim_filter.c

@@ -1900,7 +1900,8 @@ static size_t animdata_filter_gpencil(bAnimContext *ac,
       if ((filter_mode & ANIMFILTER_DATA_VISIBLE) && !(ads->filterflag & ADS_FILTER_INCL_HIDDEN)) {
         /* Layer visibility - we check both object and base,
          * since these may not be in sync yet. */
-        if ((base->flag & BASE_VISIBLE_DEPSGRAPH) == 0) {
+        if ((base->flag & BASE_VISIBLE_DEPSGRAPH) == 0 ||
+            (base->flag & BASE_VISIBLE_VIEWLAYER) == 0) {
           continue;
         }