ci: Update Stack matrix (drop GHC 8.0, 8.2, add 9.8)

The old version's aren't supported by recent version of Stack any more:

    Error: [S-5973]
      Stack builds with the version of the Cabal package that comes with the specified version of
      GHC. However, Stack no longer supports such Cabal versions before 2.2. Version 2.0.1.0 was
      found. To fix this, either use Stack 2.15.3 or earlier or use a snapshot that specifies a
      version of GHC that is 8.4 or later. Stackage LTS Haskell 12.0 (lts-12.0) or later or Nightly
      2018-03-13 (nightly-2018-03-13) or later specify such GHC versions.

And it's not worth trying to downgrade Stack to support these old
versions.

.github/workflows/stack.yml

@@ -12,8 +12,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - resolver: lts-9   # GHC 8.0
-          - resolver: lts-11  # GHC 8.2
           - resolver: lts-12  # GHC 8.4
           - resolver: lts-14  # GHC 8.6
           - resolver: lts-16  # GHC 8.8
@@ -22,6 +20,7 @@ jobs:
           - resolver: lts-20  # GHC 9.2
           - resolver: lts-21  # GHC 9.4
           - resolver: lts-22  # GHC 9.6
+          - resolver: lts-23  # GHC 9.8
 
     steps:
       - name: Clone project