CI: flatten the key restore structure

Docs:
> The cache action first searches for cache hits for `key` and `restore-keys` in the branch containing the workflow run. If there are no hits in the current branch, the cache action searches for `key` and `restore-keys` in the parent branch and upstream branches.

So the `key` matches first in any case & scenario. & because `*-bench-*` was
proven to be superflous & so removed - now we have only 1 namespace to search
through. & so we arrived at this simple solution (it is also exactly the way how cache nicely works in
repositories I manage).

Author: Anton-Latukha

.github/workflows/bench.yml

@@ -50,10 +50,7 @@ jobs:
         path: |
           ~/.cabal/packages
           ~/.cabal/store
-        restore-keys: |
-            v2-${{ runner.os }}-${{ matrix.ghc }}-build-${{ hashFiles('cabal.project') }}
-            v2-${{ runner.os }}-${{ matrix.ghc }}-build-
-            v2-${{ runner.os }}-${{ matrix.ghc }}
+        restore-keys: v2-${{ runner.os }}-${{ matrix.ghc }}-build-
 
     - run: cabal update
 

.github/workflows/cache-deps.yml

@@ -100,10 +100,7 @@ jobs:
             ${{ env.CABAL_PKGS_DIR }}
             ${{ env.CABAL_STORE_DIR }}
           key: v2-${{ runner.os }}-${{ matrix.ghc }}-build-${{ hashFiles('cabal.project') }}
-          restore-keys: |
-            v2-${{ runner.os }}-${{ matrix.ghc }}-build-${{ hashFiles('cabal.project') }}
-            v2-${{ runner.os }}-${{ matrix.ghc }}-build-
-            v2-${{ runner.os }}-${{ matrix.ghc }}
+          restore-keys: v2-${{ runner.os }}-${{ matrix.ghc }}-build-
 
       - run: cabal update
 

.github/workflows/test.yml

@@ -122,10 +122,7 @@ jobs:
           path: |
             ${{ env.CABAL_PKGS_DIR }}
             ${{ env.CABAL_STORE_DIR }}
-          key: v2-${{ runner.os }}-${{ matrix.ghc }}-build-${{ hashFiles('cabal.project') }}
-          restore-keys: |
-            v2-${{ runner.os }}-${{ matrix.ghc }}-build-
-            v2-${{ runner.os }}-${{ matrix.ghc }}
+          restore-keys: v2-${{ runner.os }}-${{ matrix.ghc }}-build-
 
       - run: cabal update