[ruby/net-http] Use omit instead of skip for test-unit

https://github.com/ruby/net-http/commit/5bb14fd3bc

test/net/http/test_httpresponse.rb

@@ -79,7 +79,7 @@ EOS
   def test_read_body_block_mod
     # http://ci.rvm.jp/results/trunk-mjit-wait@silicon-docker/3019353
     if defined?(RubyVM::JIT) ? RubyVM::JIT.enabled? : defined?(RubyVM::MJIT) && RubyVM::MJIT.enabled?
-      skip 'too unstable with --jit-wait, and extending read_timeout did not help it'
+      omit 'too unstable with --jit-wait, and extending read_timeout did not help it'
     end
     IO.pipe do |r, w|
       buf = 'x' * 1024