Fully upgrade to cabal-3.4.0.0

Author: newhoggy

.github/workflows/haskell.yml

@@ -23,18 +23,11 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - name: Select optimal cabal version
-        run: |
-          case "$OS" in
-            Windows_NT)   echo "CABAL_VERSION=3.4.0.0-rc5"  >> $GITHUB_ENV;;
-            *)            echo "CABAL_VERSION=3.4.0.0"      >> $GITHUB_ENV;;
-          esac
-
       - uses: haskell/actions/setup@v1
         id: setup-haskell
         with:
           ghc-version: ${{ matrix.ghc }}
-          cabal-version: ${{ env.CABAL_VERSION }}
+          cabal-version: 3.4.0.0
 
       - name: Set some window specific things
         if: matrix.os == 'windows-latest'