CI: Add ghc 9.12 to the build matrix

Author: erikd

.github/workflows/haskell.yml

@@ -20,7 +20,7 @@ jobs:
       matrix:
         os: [ubuntu-latest]
         # TODO: Add ghc910 when input-output-hk/devx is fixed
-        compiler-nix-name: [ghc810, ghc96, ghc98]
+        compiler-nix-name: [ghc810, ghc96, ghc98, ghc912]
         include:
           # We want a single job, because macOS runners are scarce.
           - os: macos-latest