add backdate_admonition to depwarn=error (#58266)
This is close to the expected behavior after deprecations are removed
(other than that the b->globalref->mod in the printed message here will
be the source module instead of the destination module, which may
sometimes cause confusing printing here, but probably rarely). I also
needed this recently to find a place this warning occurred, so I think
it should be merged now and get feedback later.
Closes #57969
