Update used Python versions

[egpbos]

Following this review discussion, we should add Python 3.10 support to the template. We could consider removing 3.7 support depending on when this issue gets solved; NumPy has already stopped supporting it (see https://numpy.org/neps/nep-0029-deprecation_policy.html#drop-schedule), but Python 3.7 itself is not yet end-of-life, although it will be in a little over a year (see https://endoflife.date/python).