Update Stack setup to LTS 19 (GHC 9.0.2)

[mmhat]

Greetings from ZuriHac!

[Gabriella439]

hmmm the test failures seem a bit surprising; it's not clear how they relate to the change

[mmhat]

hmmm the test failures seem a bit surprising; it's not clear how they relate to the change

I suspect that the doctest version (0.18.2; previously: 0.17) causes the trouble. I had a quick look at the changelog and the source code diff but it is not clear to me how to fix that. Someone at ZuriHac suggested to switch to cabal-docspec; I'll try that.

[mmhat]

Regarding the doctest issue: The upstream bug report is sol/doctest#327.

I tried using cabal-docspec (did not push the code to a branch yet) and while the output is much better it requires to change some tests. I am not sure if that is worth the effort if we we can get the tests running with doctest.

[mmhat]

I am closing this in favor of #2531. Supporting GHC 9.0 is IMHO not that important if we have a working setup for 9.2.