Drop ColorPrinter's workaround for BasicObject

[st0012]

pp 0.6.0+ includes ruby/pp#26 to handle BasicObject, so we can drop the workaround.

(pp supports Ruby 2.7+ too)

[st0012]

Update: Updating rubygems on CI resolves the issue.

---

Based on the debugging run's message:

Error: test_object_inspection_handles_basic_object(TestIRB::ContextTest): NameError: uninitialized constant PP::VERSION
/home/runner/work/irb/irb/test/irb/test_context.rb:161:in `test_object_inspection_handles_basic_object'
     15[8](https://github.com/ruby/irb/actions/runs/12399361528/job/34614111414?pr=1051#step:4:9):         irb.eval_input
     159:       end
     160:       assert_empty err
  => 161:       puts PP::VERSION
     162:       assert_not_match(/NoMethodError/, out)
     163:       assert_match(/#<BasicObject:.*>/, out)
     164:     ensure
Error: NameError: uninitialized constant PP::VERSION

It looks like Ruby 2.7's bundler failed to use the pp gem and still uses the one that's bundled with Ruby.

[tompng]

Do we need to specify this instead of adding it just to Gemfile for testing?
User can install bug fixed version of pp if they want (but I know user usually don't update pp nor add pp to Gemfile)
It is beneficial, but adding it is not a usual case. We don't usually bump reline or rdoc requirements for each bug fixes.
What do you think?

[st0012]

We need to specify it otherwise with the workaround removed, users with newer IRB but older pp will get a regression when dealing with basic objects.

It is beneficial, but adding it is not a usual case. We don't usually bump reline or rdoc requirements for each bug fixes.

We do when we have to make corresponding changes on IRB side?

It's like when repl_type_completor adopts new Prism APIs/structures, it bumps its requirement for prism.

We can of course make the patch conditional based on the version of pp it uses, but IMO with the size of the current patch it's not worth it.