message: Fix fetch tests on systems that already have Ninja on the PATH.
  Azure Pipelines has started putting a ninja on the PATH which causes the fetch test that assumes it needs to download ninja to fail. For example:
diff: @@ -92,7 +92,10 @@ if (-not $IsMacOS -and -not $IsLinux) {
  Require-FileNotExists "$TestingRoot/down loads/tools/ninja-1.10.2-windows/ninja.exe"
  Remove-Item env:VCPKG_FORCE_SYSTEM_BINARIES
  - Run-Vcpkg -TestArgs ($commonArgs + @("fetch", "ninja", "--vcpkg-root=$TestingRoot"))
  + $out = Run-Vcpkg -TestArgs ($commonArgs + @("fetch", "ninja", "--vcpkg-root=$TestingRoot", "--x-stderr-status"))
  Throw-IfFailed
  - Require-FileExists "$TestingRoot/down loads/tools/ninja-1.10.2-windows/ninja.exe"
  + & $out --version
  + if ($LASTEXITCODE -ne 0) {
  + throw 'Couldn''t run resulting ninja'
  + }
  }
  