Replace deprecated `np.object` with `object`.
Replace deprecated `np.object` with `object`.

Please see https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations.

PiperOrigin-RevId: 463921446
Change-Id: Ia89ff3e84dbec260114ef9128356dc1513ffe7b8

deepmind/envlogger,deepmind/envlogger,deepmind/envlogger,deepmind/envlogger