When creating a new action slot for a data-block, via the '+ New' button
of the slot selector, use the name of the slot that was last used by
that data-block. Previously, it would always use the name of the
data-block, interfering with slot auto-selection when toggling between
Actions.
Pull Request: https://projects.blender.org/blender/blender/pulls/138326
f6167aab31