Randomize stdlib test order to uncover hidden assumptions

[soutaro]

#2042 didn't reproduce in our CI, because Net_HTTP_test.rb sets $stdout between Kernel_test.rb and Open3_test.rb. CI in ruby/ruby skips the Net::HTTP tests to avoid unpredictable result caused by external network request, which uncovered the $stdout reset problem.

I hope randomizing the testing order will uncover this kind of problems.

[soutaro]

Is it reporting a true problem??? 👀

Failure: test_accept_charset(CGISingletonTest):
  Call trace does not match with given method type: #<struct RBS::Test::CallTrace method_name=:accept_charset, method_call=<RBS::Test::ArgumentsReturn:@arguments: [], @exit_value: #<Encoding:UTF-8>, @exit_type: :return>, block_calls=[], block_given=false>.
  <["[Class#accept_charset] ReturnTypeError: expected `::String` but returns `#<Encoding:UTF-8>`"]> was expected to be empty.
/home/runner/work/rbs/rbs/lib/rbs/unit_test/type_assertions.rb:183:in 'block in RBS::UnitTest::TypeAssertions#assert_send_type'
/home/runner/work/rbs/rbs/lib/rbs/unit_test/type_assertions.rb:168:in 'RBS::UnitTest::TypeAssertions#send_setup'
/home/runner/work/rbs/rbs/lib/rbs/unit_test/type_assertions.rb:172:in 'RBS::UnitTest::TypeAssertions#assert_send_type'
test/stdlib/CGI_test.rb:25:in 'CGISingletonTest#test_accept_charset'

[soutaro]

The problem will be fixed by #2045.