CI: Add ghc-9.8 to build matrix

Author: erikd

.github/workflows/haskell.yml

@@ -19,7 +19,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        compiler-nix-name: [ghc810, ghc96]
+        compiler-nix-name: [ghc810, ghc96, ghc98]
         include:
           # We want a single job, because macOS runners are scarce.
           - os: macos-latest