bump upper limit on unix dependency

[peterbecich]

Currently, certain Cabal packages allow unix 2.8.6.*, and others do not.

This PR changes the latter so all can use unix 2.8.6.*. The test:

cabal build all --enable-tests --constraint 'unix==2.8.6.0'

succeeds

Template B: This PR does not modify behaviour or interface

E.g. the PR only touches documentation or tests, does refactorings, etc.

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Is this a PR that fixes CI? If so, it will need to be backported to older cabal release branches (ask maintainers for directions).

[Bodigrim]

Are they real packages though? Seems just input data for parser tests, no?

[peterbecich]

@Bodigrim you're correct, thanks! That explains the test failure