Suppress deprecation warning for `Regexp.new` with 3rd argument

[koic]

Follow up https://github.com/ruby/ruby/pull/6976.

This PR suppresses the following deprecation warning.

% ruby -v
ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-darwin19]
% bundle exec rake
(snip)

/Users/koic/src/github.com/dwaite/cookiejar/lib/cookiejar/cookie_validation.rb:48: warning:
3rd argument to Regexp.new is deprecated and will be removed in Ruby 3.3; use 2nd argument instead

[yahonda]

I want this pull request merged because this behavior gets error at Ruby 3.3.0dev since https://github.com/ruby/ruby/pull/7039 .

Rails 7.0.z needs blade gem and the CI is failing. https://buildkite.com/rails/rails/builds/94669#0186dc1f-05f9-4363-b83c-95d392a7c5d9/3376-3379

Rails 7.0.z depends on blade gem. Then blade gem indirectly depends on cookiejar via these gems like that: blade -> faye -> em-http-request -> cookiejar

[koic]

Yeah, that's exactly it! @dwaite Could you review this PR and cut a new release if it is fine with you?