Replace deprecated numpy dtypes np.bool and np.int

[santisoler]

Description

Numpy dtypes like np.bool and np.int have been deprecated since Numpy v1.2.0 in favor of using
builtin bool or int, or even np.int64 and np.int32 which explicitly
sets their precision.

See https://numpy.org/devdocs/release/1.20.0-notes.html#using-the-aliases-of-builtin-types-like-np-int-is-deprecated
for a list of deprecated data types.

[leouieda]

Failing because pytest dropped 3.6... Let's get rid of it too and then merge this.