Update pullrequest-ci.yml and hopefully fix cache

Author: BinderDavid

.github/workflows/pullrequest-ci.yml

@@ -9,29 +9,44 @@ jobs:
   build-and-test:
     name: Build site
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ghc: ["9.2.5"]
+        cabal: ["3.10.1"]
+    
+    defaults:
+      run:
+        working-directory: message-index
 
     steps:
-    - name: Install GHC 9.2.5
-      run: ghcup install ghc 9.2.5
-
-    - name: Select GHC 9.2.5
-      run: ghcup set ghc 9.2.5
-
     - name: Check out repo
       uses: actions/checkout@v3
+
+    - name: Install Haskell Toolchain
+      uses: haskell/actions/setup@v2
+      with:
+        ghc-version: ${{ matrix.ghc }}
+        cabal-version: ${{ matrix.cabal }}
+
+    - name: Configure the build plan
+      run: |
+        cabal update
+        cabal build --dry-run
+      # cabal build --dry-run creates dist-newstyle/cache/plan.json
+      # Keep a watch on this `cabal-3.9 build --dry-run` bug:
+      # https://github.com/haskell/cabal/issues/8706
 
     - name: Read the Cabal cache
       uses: actions/cache@v3
       with:
         path: |
           ~/.cabal/store
           message-index/dist-newstyle
-        key: cabal-cache-0-${{ hashFiles('message-index/message-index.cabal') }}
+        key: |
+          cabal-cache-ghc-${{ matrix.ghc }}-cabal-${{ matrix.cabal }}-${{ hashFiles('**/plan.json') }}
         restore-keys: |
-          cabal-cache-0
+          cabal-cache-ghc-${{ matrix.ghc }}-cabal-${{ matrix.cabal }}-
 
-    - name: Update the Cabal index
-      run: cabal update
 
     - name: Build with Hakyll
       working-directory: message-index