`array_api_strict.asarray` does not raise for nested sequence of arrays

[mdhaber]

IIUC, asarray must support nested sequences of Python scalars, but not a nested sequence of arrays.

asarray raises on a sequence of arrays:

import array_api_strict as xp
xp.asarray([xp.asarray(1)])
# TypeError: Nested Arrays are not allowed. Use `stack` instead.

But not a nested sequence of arrays:

xp.asarray([[xp.asarray(1)]])
# Array([[1]], dtype=array_api_strict.int64)

Crossref data-apis/array-api-tests#461