ci: fix cache key

Author: drlkf

.github/workflows/stack-build.yml

@@ -51,18 +51,22 @@ jobs:
           stack-no-global: true
 
       - name: Configure the build
+        id: configure
         run: |
-          echo "with key: ${{ runner.os }}-ghc-${{ steps.setup.outputs.ghc-version }}-cabal-${{ steps.setup.outputs.cabal-version }}"
+          echo "with key: ${{ runner.os }}-lts-${{ matrix.stack.lts }}"
 
           stack config set resolver lts-${{ matrix.stack.lts }}
           stack build --dry-run
           # The last step generates dist-newstyle/cache/plan.json for the cache key.
 
+        outputs:
+          cache-key: ${{ runner.os }}-lts-${{ matrix.stack.lts }}
+
       - name: Restore cached dependencies
         uses: actions/cache/restore@v3
         id: cache
         env:
-          key: ${{ runner.os }}-ghc-${{ steps.setup.outputs.ghc-version }}-cabal-${{ steps.setup.outputs.cabal-version }}
+          key: ${{ steps.configure.outputs.cache-key }}
 
         with:
           path: ${{ steps.setup.outputs.stack-root }}
@@ -72,7 +76,8 @@ jobs:
       - name: Install dependencies
         run: stack build --only-dependencies
 
-      # Cache dependencies already here, so that we do not have to rebuild them should the subsequent steps fail.
+      # Cache dependencies already here, so that we do not have to rebuild them
+      # should the subsequent steps fail.
       - name: Save cached dependencies
         uses: actions/cache/save@v3
         # Caches are immutable, trying to save with the same key would error.