Try to install the missing zstd on macOS-14

Author: dabrahams

.github/workflows/build-and-test.yml

@@ -190,6 +190,7 @@ jobs:
           - windows_only: '# WINDOWS ONLY:'
           - on_windows_and_spm_works: false
           - use_spm: true
+          - zstd_installation_command: ''
 
           - os: windows-latest
             unpackage_command: 7z x -t7z
@@ -202,6 +203,7 @@ jobs:
 
           - os: macos-14
             triple_suffix: apple-darwin24.1.0
+            zstd_installation_command: brew install zstd
 
           - os: ubuntu-latest
             triple_suffix: unknown-linux-gnu
@@ -265,6 +267,8 @@ jobs:
         # 7z doesn't support decompressing from a stream or we'd do this all as one statement. Maybe
         # we should find a way to use zstd on windows.
         run: >-
+          ${{ matrix.zstd_installation_command }}
+          
           curl --no-progress-meter -L -O
           -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}"
           ${{ env.llvm_url_prefix }}/${{ env.llvm_package_basename }}${{ matrix.llvm_package_suffix }}