jruby: mri-extra - flaky TestOpen3 pipe tests

The autopkgtests for jruby fail `mri-extra` with the following errors:

  1) Failure:
TestOpen3#test_pipeline_start [/tmp/autopkgtest.Dz4xQk/autopkgtest_tmp/test/mri/test_open3.rb:303]:
Failed assertion, no message given.

  2) Failure:
TestOpen3#test_pipeline_w [/tmp/autopkgtest.Dz4xQk/autopkgtest_tmp/test/mri/test_open3.rb:288]:
<true> expected but was
<false>.

  3) Failure:
TestOpen3#test_capture3_flip [/tmp/autopkgtest.Dz4xQk/autopkgtest_tmp/test/mri/test_open3.rb:190]:

The minimal reproducer of those:
----
require 'open3'

RUBY = 'jruby'
Open3.pipeline_r([RUBY, '-e', 'print "1"'],
                     [RUBY, '-e', 'print STDIN.read + "2"']) {|o,ts|
      print(o.read)
    }
---

executing the above sample results in the following output:
# jruby test.rb
12# jruby test.rb
12# jruby test.rb
12# jruby test.rb
12# jruby test.rb
2# jruby test.rb
12# jruby test.rb
2# jruby test.rb
12# jruby test.rb
2# jruby test.rb
2# jruby test.rb
2# jruby test.rb
2# jruby test.rb
12# jruby test.rb
12# jruby test.rb
2Errno::EPIPE: Broken pipe - <STDOUT>
   write at org/jruby/RubyIO.java:1569
   write at org/jruby/RubyIO.java:1458
   write at org/jruby/RubyIO.java:2829
   print at org/jruby/RubyIO.java:1831
   print at org/jruby/RubyKernel.java:649
  <main> at -e:1

Note: the failure occurs both with Java 21
The root cause is that pipes are created non-blocking with Java 21.

The workaround for the stream issue is below:
----

require 'fcntl'
flags = write.fcntl(Fcntl::F_GETFL)
# We must first set nonblock because the Java and JRuby objects wrapping the stream do not know it is already non-blocking
write.fcntl(Fcntl::F_SETFL, flags | (Fcntl::O_NONBLOCK))
write.fcntl(Fcntl::F_SETFL, flags & (~Fcntl::O_NONBLOCK))
----