interperterbase: help type checkers do better type deduction
interperterbase: help type checkers do better type deduction

This assert causes several type checkers (both mypy and pyright) to
force `obj` to be a base `HoldableObject` instead of the specialized
object. Since the check itself may still be valuable as we don't have
fully type annotation coverage it's simply been removed when type
checking to aid in type specialization.

mesonbuild/meson,pexip/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,pexip/meson,pexip/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,mesonbuild/meson,pexip/meson,mesonbuild/meson,pexip/meson