CI: Update stackage resolvers

+ Drop lts-14 and thus GHC 8.6 support.
+ Update lts-{18,19} to the respective newest minor versions.
+ Add lts-20 for GHC 9.2.
+ Add nightly-2023 for GHC 9.4

.github/workflows/haskell-ci.yml

@@ -14,7 +14,7 @@ jobs:
  fail-fast: false
  matrix:
  os: [windows-latest, ubuntu-latest, macos-latest]
- resolver: [lts-14.27, lts-16.31, lts-18.15, lts-19.0, nightly-2022-03-21]
+ resolver: [lts-16.31, lts-18.28, lts-19.33, lts-20.5, nightly-2023-01-03]
 
  steps:
  - name: Clone project