Bug#970510: why3: does not work with current version of cvc4

[Fabian Wolff <fabi.wolff@arcor.de>]

And while we're at it, even though this is technically an unrelated
problem, it also has something to do with SMT solver versions: In the
autopkgtests control file [0], you have the following code:

  Tests: why3+z3
  Depends:why3, z3 (<< 4.8.7)
  Restrictions: skip-not-installable

This is not a big issue, because it doesn't block migration of z3
(unlike the cvc4 failure [1]), you might still want to adjust this
version restriction, given that the current z3 version in unstable is
4.8.9 (unless, of course, there is a reason why why3 won't work with
more recent versions of z3).

Thanks!

Fabian

[0] https://sources.debian.org/src/why3/1.3.2-1/debian/tests/control/#L13
[1] https://lists.debian.org/debian-ci/2020/09/msg00042.html