Suppress warning for intentional circular require

[ntkme]

If ruby was started in verbose mode, it prints this warning:

$ ruby -w -r google/protobuf -e ''
<internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85: warning: <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85: warning: loading in progress, circular require considered harmful - /usr/local/bundle/gems/google-protobuf-3.19.4/lib/google/protobuf.rb
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:149:in  `require'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:160:in  `rescue in require'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:160:in  `require'
        from /usr/local/bundle/gems/google-protobuf-3.19.4/lib/google/protobuf.rb:57:in  `<top (required)>'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85:in  `require'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85:in  `require'
        from /usr/local/bundle/gems/google-protobuf-3.19.4/lib/google/protobuf/descriptor_dsl.rb:5:in  `<top (required)>'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85:in  `require'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85:in  `require'
        from /usr/local/bundle/gems/google-protobuf-3.19.4/lib/google/protobuf/descriptor_pb.rb:4:in  `<top (required)>'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85:in  `require'
        from <internal:/usr/local/lib/ruby/3.1.0/rubygems/core_ext/kernel_require.rb>:85:in  `require'

The circular require is:

protobuf.rb -> protobuf/descriptor_dsl.rb -> protobuf/descriptor_pb.rb -> protobuf.rb

It is very annoying that many ruby test framework (e.g. minitest) runs in ruby verbose mode by default and thus prints this message every time the test runs.

As far as I can see, this circular require is actually needed. It guarantees that if user requires any one of the three files, all three files will be loaded. Since we intentionally need this circular require, it's best to just suppress the warning here, rather than having the user dealing with figure out how to suppress this one warning with other warnings untouched.

[haberman]

Related: #9355

I think suppressing the warning makes sense until we can implement a more principled fix.