Following T54811: COW Operators: Edit Armature (and rBbb92edd1c802: Depsgraph: Keep edit bones around, fixes missing edit mode with copy on write), DEG updates have been added
to the various operators. This has also been done for the layers
operators (see rBf998bad211ae: Fix: Last of the operators from T54811 now work with Copy on Write, ARMATURE_OT_bone_layers has been
marked done in T54811). However, instead of ARMATURE_OT_bone_layers,
the update tagging actually happened for POSE_OT_bone_layers.
Now do this for ARMATURE_OT_bone_layers as well (keep it for
POSE_OT_bone_layers, dont think this is wrong there either).