Fix github workflow.

Author: qnikst

.github/workflows/haskell.yml

@@ -22,7 +22,7 @@ jobs:
     - uses: actions/checkout@v2
     - uses: actions/setup-haskell@v1
       with:
-        ghc-version: ${{ matrics.ghc }}
+        ghc-version: ${{ matrix.ghc }}
         cabal-version: ${{ matrix.cabal }}
 
     - name: Cache