rake test fails with Minitest 6.0.5 with incorrect assert_raises usage

[mtasaka]

Even with #38 is applied, now With Minitest 6.0.5 rake test fails like:

# Running:

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Finished in 0.183250s, 2575.7125 runs/s, 5511.5882 assertions/s.

  1) Error:
TestStubbing#test_based_partial_mocks_require_explicitly_on_a_non_existing_method_of_a_class_singleton:
TypeError: class or module required for rescue clause. Got [NoMethodError, /bark.*explicitly/]
    test/partial_mock_test.rb:500:in 'TestStubbing#test_based_partial_mocks_require_explicitly_on_a_non_existing_method_of_a_class_singleton'

  2) Error:
TestStubbing#test_partial_mocks_disallow_stubbing_undefined_methods_when_using_on:
TypeError: class or module required for rescue clause. Got [NoMethodError, /meow.*explicitly/]
    test/partial_mock_test.rb:460:in 'TestStubbing#test_partial_mocks_disallow_stubbing_undefined_methods_when_using_on'

  3) Error:
TestStubbing#test_partial_mocks_require_explicitly_on_a_class_singleton_method_that_has_been_mocked_on_the_parent_class:
TypeError: class or module required for rescue clause. Got [NoMethodError, /bark.*explicitly/]
    test/partial_mock_test.rb:514:in 'TestStubbing#test_partial_mocks_require_explicitly_on_a_class_singleton_method_that_has_been_mocked_on_the_parent_class'

  4) Error:
BasedPartialsTest#test_based_partials_disallow_stubbing_undefined_methods:
TypeError: class or module required for rescue clause. Got [NoMethodError, /cannot stub.*wag.*explicitly/]
    test/based_partials_test.rb:49:in 'BasedPartialsTest#test_based_partials_disallow_stubbing_undefined_methods'

472 runs, 1010 assertions, 0 failures, 4 errors, 0 skips
rake aborted!