[Chore] Use LTS-21

[gromakovsky]

Description

This PR updated the Stackage resolver to the latest one and does some related cleaning.

Related issue(s)

Resolves #285

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Related changes (conditional)

• Tests

  • [x] If I added new functionality, I added tests covering it.
  • [x] If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.

• Documentation

  • [x] I checked whether I should update the docs and did so if necessary:
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  • [x] Any modifications of public contracts comply with the Evolution of Public Contracts policy.
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Stylistic guide (mandatory)

• [x] My commits comply with the policy used in Serokell.
• [x] My code complies with the style guide.

✓ Release Checklist

• [ ] I updated the version number in package.yaml.
• [ ] I updated the changelog and moved everything under the "Unreleased" section to a new section for this release version.
• [ ] (After merging) I edited the auto-release.
  • Change the tag and title using the format vX.Y.Z.
  • Write a summary of all user-facing changes.
  • Deselect the "This is a pre-release" checkbox at the bottom.
• [ ] (After merging) I updated xrefcheck-action.
• [ ] (After merging) I uploaded the package to hackage.

[serokell-bot]

	3 Warnings
:warning:	In d012849441590c9c5890ec45e272f02f97076062 message lacks issue id: Automatically update flake.lock to the latest version. See also [Note].
:warning:	Description of d012849441590c9c5890ec45e272f02f97076062 does not follow the template. Try Problem:/Solution: structure. If you really have to, you can add And yes, I don't care about templates to the commit message body. See also [Note].
:warning:	Bad issue ID in branch name. Valid format for issue IDs: #123 or chore.

[Note]: Skip this check by adding wip, tmp or [temporary] to the commit subject. Fixup commits (marked with fixup! or squash!) are also exempt from this check.

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[Martoon-00]

CI is failing due to warnings / compilation errors also related to LTS-21. Other than that, LGTM.

[gromakovsky]

@Martoon-00 if you volunteer to fix them by any chance, feel free to go ahead :wink:

[Martoon-00]

Okay, I fixed the errors that I saw (note there are fixup commits, you may want to squash them after reviewing them).

However now some really scary errors bumped up, and I have to switch to other activities, so giving up on this right now.

[gromakovsky]

note there are fixup commits, you may want to squash them after reviewing them

Reviewed, squashed.

Also updated the resolver to a bit newer one, so that a newer minor GHC version is used. Let's see if it helps with any of scary errors. UPD: there are still some weird errors, not sure if it helped with any of them, but definitely not with all of them.

[serokell-bot]

	1 Error
:no_entry_sign:	Some fixup commits are still there.

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