Unpin cffi from version < 1.17

[schnellerhase]

The release of cffi version v1.17.0 broke the red hat CI pipeline.

An explicit downgrade as hot fix was introduced in #3339. This should be reverted, to using the latest version of cffi in its runs, to fix this issue.

Interestingly this seems to be a platform dependent problem as the other CI runs did not reproduce the behavior.

[garth-wells]

Unpin once python-cffi/cffi#111 is in cffi release.

See also python-cffi/cffi#127.

[francesco-ballarin]

Just a heads up that on my Debian testing system cffi<1.17 failed to compile from source with python 3.13, while cffi==1.17 works fine (and is already packaged). The pin should ideally be gone before our next release if at all possible (meaning, if cffi does have a new release in the meantime).

[garth-wells]

We should unpin cffi now, and raise an exception if a user tries to use it with a complex type (and advise them to rollback cffi).