CI: bench: use env

Author: Anton-Latukha

.github/workflows/bench.yml

@@ -61,8 +61,8 @@ jobs:
       uses: actions/cache@v2
       with:
         path: |
-          ~/.cabal/packages
-          ~/.cabal/store
+          ${{ env.CABAL_PKGS_DIR }}
+          ${{ env.CABAL_STORE_DIR }}
         key: v2-${{ runner.os }}-${{ matrix.ghc }}-bench-${{ hashFiles('cabal.project') }}
         restore-keys: |
             v2-${{ runner.os }}-${{ matrix.ghc }}-build-${{ hashFiles('cabal.project') }}