Fix nightly build failures

[neilmayhew]

Description

• Fix nightly build failures
• Allow simulating a nightly build when manually triggering a build

Checklist

• [x] Commit sequence broadly makes sense and commits have useful messages
• [ ] New tests are added if needed and existing tests are updated
• [ ] When applicable, versions are updated in .cabal and CHANGELOG.md files according to the versioning process.
• [ ] The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• [ ] All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• [x] Code is formatted with fourmolu (use scripts/fourmolize.sh)
• [x] Cabal files are formatted (use scripts/cabal-format.sh)
• [x] hie.yaml has been updated (use scripts/gen-hie.sh)
• [x] Self-reviewed the diff

[lehins]

There are still flaky tests that are failing to discards. But, it is one step closer to nightly builds going green

[neilmayhew]

Looks good to me. In case it's easier to test: I have used a fork repo to play with the build and actions, to keep the things needed just for testing separate from what I wanted to merge (just in case the idea is useful to you too)

Thanks! That's a great idea. It looks like I don't need it for now, but I'll definitely keep that in mind for the future.

[neilmayhew]

@lehins Would you do an admin merge, please? I can't get this to pass all of the matrix builds at the same time, since it's running the nightly tests.

Also, it takes so long to run that master has usually been updated by the time I can run it again. However, it should rebase cleanly on top of the changes merged to master today.

[lehins]

@neilmayhew Sounds good. I'll take care of merging this PR.