Exclude transient MRI test

Author: eregon

test/mri/excludes/TestAutoload.rb

@@ -1,3 +1,4 @@
 exclude :test_source_location, "needs investigation"
 exclude :test_threaded_accessing_inner_constant, "Exception raised:"
 exclude :test_autoload_parent_namespace, "expected: /\\/some_const.rb to define SomeNamespace::SomeConst but it didn't/"
+exclude :test_autoload_parallel_race, "transient timeout"