Drop undefiend variable in CI

It's not defined and expands to empty string. CI works so we can
simply drop it.

Fixes #526

Author: Shimuuar

.github/workflows/ci.yml

@@ -74,7 +74,7 @@ jobs:
       name: Cache ~/.cabal/store
       with:
         path: ${{ steps.setup-haskell-cabal.outputs.cabal-store }}
-        key: ${{ runner.os }}-${{ matrix.ghc }}--${{ github.Shah }}-CACHE_V3
+        key: ${{ runner.os }}-${{ matrix.ghc }}---CACHE_V3
     # ----------------
     - name: "Install PAPI"
       run: |