Fix some WWDR certificates test failure

This was caused by the fact that that test calls a method that uses `$?`
(https://stackoverflow.com/a/6834572/865175), which, somehow, (I think)
was executed right after a call to XcodesHelper's
`find_xcodes_binary_path` method. This latter one returned a non-zero
code, because `xcodes` can't be installed on Ubuntu, which got picked up
by the certificates return code check, so it treated its actual command
as failed.

fastlane/lib/fastlane/helper/xcodes_helper.rb

@@ -12,7 +12,7 @@ def self.read_xcode_version_file
       end
 
       def self.find_xcodes_binary_path
-        `which xcodes`.strip
+        Actions.sh("which xcodes", log: false).strip
       end
 
       module Verify