`assert_linear_performance` fail with Ruby head on windows

[st0012]

Example from RDoc (build)

Error: test_read_directive_linear_performance(RDocParserRubyTest): TypeError: nil can't be coerced into Integer
D:/a/rdoc/rdoc/vendor/bundle/ruby/3.5.0+4/gems/test-unit-ruby-core-1.0.10/lib/core_assertions.rb:871:in 'Integer#*'
D:/a/rdoc/rdoc/vendor/bundle/ruby/3.5.0+4/gems/test-unit-ruby-core-1.0.10/lib/core_assertions.rb:871:in 'Test::Unit::CoreAssertions#assert_linear_performance'
D:/a/rdoc/rdoc/test/rdoc/rdoc_parser_ruby_test.rb:3384:in 'RDocParserRubyTest#test_read_directive_linear_performance'
     3381:   def test_read_directive_linear_performance
     3382:     omit "JRuby intermittently times out" if RUBY_ENGINE == 'jruby'
     3383:     pre = ->(i) {util_parser '# ' + '0'*i + '=000:'}
  => 3384:     assert_linear_performance((1..5).map{|i|10**i}, pre: pre) do |parser|
     3385:       assert_nil parser.read_directive []
     3386:     end
     3387:   end

Example from net-imap (rerun on a previously succeeded build)

Error: test_digest_md5_authenticator_illinear(AuthenticatorsTest): TypeError: nil can't be coerced into Integer
D:/a/net-imap/net-imap/vendor/bundle/ruby/3.5.0+4/bundler/gems/test-unit-ruby-core-64837e6f0d40/lib/core_assertions.rb:871:in 'Integer#*'
D:/a/net-imap/net-imap/vendor/bundle/ruby/3.5.0+4/bundler/gems/test-unit-ruby-core-64837e6f0d40/lib/core_assertions.rb:871:in 'Test::Unit::CoreAssertions#assert_linear_performance'
D:/a/net-imap/net-imap/test/net/imap/test_authenticators.rb:517:in 'AuthenticatorsTest#test_digest_md5_authenticator_illinear'
     514: 
     515:   def test_digest_md5_authenticator_illinear
     516:     pre = ->(n) {'qop="a' + ',x'*n}
  => 517:     assert_linear_performance([5, 10, 15, 20], pre: pre) do |challenge|
     518:       auth = digest_md5("user", "pass")
     519:       assert_raise(Net::IMAP::DataFormatError) do
     520:         auth.process(challenge)

I think it only started in the last 2 weeks and is probably a Ruby issue. But I don't have a windows machine so I can't effectively bisect which commit caused it atm. Logging now in case other people are seeing this too.

[st0012]

Thanks to @tompng, we found that it's related to ruby/ruby#14866