Modified CI workflow to exclude macOS with older Stack LTS versions

Updated GitHub Actions workflow to skip execution on macOS for Stack LTS versions 19.33 and 18.28.
Removed step for installing LLVM@13 as it's no longer supported and not needed for the current setup.
Modified the matrix strategy in the stack job to exclude specific OS and Stack version combinations to avoid compatibility issues.

.github/workflows/tests.yml

@@ -24,21 +24,17 @@ jobs:
           - 20.26 9.2.8
           - 19.33 9.0.2
           - 18.28 8.10.7
+        exclude:
+          - os: macos-latest
+            versions: 19.33 9.0.2
+          - os: macos-latest
+            versions: 18.28 8.10.7
     steps:
       - name: Parse lts and ghc versions
         shell: sh
         run: |
           echo snapshot=$(echo ${{ matrix.versions }} | cut -d ' ' -f 1) >> $GITHUB_ENV
           echo ghcVersion=$(echo ${{ matrix.versions }} | cut -d ' ' -f 2) >> $GITHUB_ENV
-      - name: Install LLVM 13
-        if: ${{ matrix.os == 'macos-latest' && env.snapshot < 20 }}
-        shell: sh
-        run: |
-          brew install llvm@13
-          echo "/opt/homebrew/opt/llvm@13/bin" >> $GITHUB_PATH
-          echo extraLibDirs="--extra-lib-dirs /opt/homebrew/opt/llvm@13/lib" >> $GITHUB_ENV
-          echo extraIncludeDirsLLVM="--extra-include-dirs /opt/homebrew/opt/llvm@13/include" >> $GITHUB_ENV
-          echo extraIncludeDirsFFI="--extra-include-dirs /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/ffi" >> $GITHUB_ENV
       - name: Setup Haskell
         id: setup-haskell-stack
         uses: haskell-actions/[email protected]