fix mtl >= 2.3 GitHub Action

Author: peterbecich

.github/workflows/cabal-mtl-2.3.yml

@@ -33,3 +33,27 @@ jobs:
         run: cabal test all --enable-tests
       - name: Haddock
         run: cabal haddock all
+  build_with_mtl_2_3:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        ghc: ['9.4.4']
+        cabal: ['3.8.1.0']
+        os: [ubuntu-latest]
+    name: Cabal with GHC ${{ matrix.ghc }} and mtl >= 2.3.1
+    steps:
+      - uses: actions/checkout@v3
+      - name: Setup Haskell
+        uses: haskell/actions/setup@v2
+        with:
+          ghc-version: ${{ matrix.ghc }}
+          cabal-version: ${{ matrix.cabal }}
+      - name: Install dependencies
+        run: sudo apt install -y libbrotli-dev libgd-dev
+      - name: Build dependencies with mtl >= 2.3.1
+        # 2022-12-30: 'transformers >= 0.6' is needed because of happstack-server
+        run: cabal build all --disable-tests --dependencies-only -O0 --constraint 'mtl >= 2.3.1' --constraint 'transformers >= 0.6' --allow-newer='Cabal:mtl' --allow-newer='Cabal:transformers'
+      - name: Build with mtl >= 2.3.1
+        # 2022-12-30: 'transformers >= 0.6' is needed because of happstack-server
+        run: cabal build all --disable-tests -O0 --constraint 'mtl >= 2.3.1' --constraint 'transformers >= 0.6' --allow-newer='Cabal:mtl' --allow-newer='Cabal:transformers'