Consider avoiding partial pattern matches in tests

[fosskers]

GHC 8.6 is more strict that 8.4 regarding its analysis of incomplete pattern matches. I think this helps us more than it hinders us, as it lets us avoid foot-gun in the long term.

In the short term, this strictness causes warnings, and a few compilation errors. In particular, the following 4 locations in the test suites trigger errors involving missing MonadFail instances (arising from partial pattern matches):

• https://github.com/kadena-io/pact/blob/master/tests/Analyze/Gen.hs#L592
• https://github.com/kadena-io/pact/blob/master/tests/Analyze/Gen.hs#L552
• https://github.com/kadena-io/pact/blob/master/tests/Analyze/Gen.hs#L453
• https://github.com/kadena-io/pact/blob/master/tests/Analyze/Gen.hs#L257

See #494 for a branch where the errors can easily be reproduced.

We can approach a solution in few ways:

1. Hope that this PR to hedgehog fixes all four issues (see also this issue for more info)
2. Avoid the partial matches ourselves