Fix crash in test runner on timeout

When a test worker hangs and timeouts, the test runner crashes with the
following stack trace:

ruby/tool/lib/test/unit.rb:1747:in `puke': undefined method `backtrace' for Timeout::Error:Class (NoMethodError)
	from ruby/tool/lib/test/unit.rb:790:in `block in _run_parallel'
	from ruby/tool/lib/test/unit.rb:788:in `each'

This commit adds handling for Timeout::Error and outputs a message.

Author: peterzhu2118

tool/lib/test/unit.rb

@@ -787,7 +787,7 @@ def _run_parallel suites, type, result
           unless rep.empty?
             rep.each do |r|
               if r[:error]
-                puke(*r[:error], Timeout::Error)
+                puke(*r[:error], Timeout::Error.new)
                 next
               end
               r[:report]&.each do |f|
@@ -1742,6 +1742,9 @@ def puke klass, meth, e
             when Test::Unit::AssertionFailedError then
               @failures += 1
               "Failure:\n#{klass}##{meth} [#{location e}]:\n#{e.message}\n"
+            when Timeout::Error
+              @errors += 1
+              "Timeout:\n#{klass}##{meth}\n"
             else
               @errors += 1
               bt = Test::filter_backtrace(e.backtrace).join "\n    "