Upgrade Aesara and NumPy upper version limits

[michaelosthege]

Aesara is currently pinned and can't be updated to the latest version until aesara-devs/aesara#707 is fixed.

That means we also don't get the NumPy 1.22 compatibility fix until we can upgrade.

Until that Aesara upgrade we'll want to pin numpy<1.22.0 and keep this issue open until we can upgrade Aesara and remove the NumPy version pin.

For stability, we should still pin Aesara at the minor, or even the patch version.

[twiecki]

aesara-devs/aesara#707 is fixed now and has an aesara release 2.3.5 https://github.com/aesara-devs/aesara/releases/tag/rel-2.3.5 which we should pin.

[twiecki]

We should cut a new release. CC @michaelosthege