run declarative scan for non-mapped annotated if allow_unmapped

run declarative scan for non-mapped annotated if allow_unmapped

Fixed issue where the ``__allow_unmapped__`` directive failed to allow for
legacy :class:`.Column` / :func:`.deferred` mappings that nonetheless had
annotations such as ``Any`` or a specific type without ``Mapped[]`` as
their type, without errors related to locating the attribute name.

issue is not ticketed yet but is coming

Fixes: #10516
Change-Id: I471d6838f4dcc113addd284a39a5bb0b885b64ea