Extend cache key with the cabal-version (#462)

Avoids cache poisoning across CI jobs.

Author: fendor

.github/workflows/haskell.yml

@@ -50,7 +50,7 @@ jobs:
           ~/.cabal/packages
           ~/.cabal/store
           dist-newstyle
-        key: ${{ runner.os }}-${{ matrix.ghc }}-${{ hashFiles('**/*.cabal', '**/cabal.project', '**/cabal.project.freeze') }}
+        key: ${{ runner.os }}-${{ matrix.cabal }}-${{ matrix.ghc }}-${{ hashFiles('**/*.cabal', '**/cabal.project', '**/cabal.project.freeze') }}
         restore-keys: ${{ runner.os }}-${{ matrix.ghc }}-
 
     - run: cabal update