Increase reliability of MacOS pipeline

azure-pipelines/steps/build_mac.yml

@@ -23,6 +23,10 @@ steps:
     displayName: 'Create Build Directory'
   - bash: |
       curl -L -o ninja-mac.zip $(curl -s https://api.github.com/repos/ninja-build/ninja/releases/latest | grep "browser_download_url.*mac\.zip" | cut -d : -f 2,3 | tr -d '"')
+      # Fallback to version 1.9.0 if the previous request fails for some reason
+      if [ ! -f /tmp/foo.txt ]; then
+        curl -L -o ninja-mac.zip https://github.com/ninja-build/ninja/releases/download/v1.9.0/ninja-mac.zip
+      fi
       unzip ninja-mac.zip -d /Users/git-bin/gtk/inst/bin
     displayName: 'Get Ninja'
   - bash: |