Skip rbs gem validation

[soutaro]

I'm not sure the reason exactly, but rbs validate with rbs fails because Gem::Specification.find_by_name('rbs') doesn't work with gemspec source with extensions.

/Users/soutaro/Developer/rbs/lib/rbs/environment_loader.rb:133:in `block in each_dir': Cannot find type definitions for library: rbs ([nil]) (RBS::EnvironmentLoader::UnknownLibraryError)

We can reproduce the problem with irb.

$ bundle exec irb
Ignoring rbs-3.7.0.dev.0 because its extensions are not built. Try: gem pristine rbs --version 3.7.0.dev.0
irb(main):001> Gem::Specification.find_by_name("rbs")
/Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/3.3.0/rubygems/dependency.rb:303:in `to_specs': Could not find 'rbs' (>= 0) - did find: [rbs-3.7.0.dev.0] (Gem::MissingSpecVersionError)
Checked in 'GEM_PATH=/Users/soutaro/.local/share/gem/ruby/3.3.0:/Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0' , execute `gem env` for more information
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/3.3.0/rubygems/dependency.rb:313:in `to_spec'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/3.3.0/rubygems/specification.rb:962:in `find_by_name'
	from (irb):1:in `<main>'
	from <internal:kernel>:187:in `loop'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/irb-1.13.1/exe/irb:9:in `<top (required)>'
	from /Users/soutaro/.rbenv/versions/3.3.6/bin/irb:25:in `load'
	from /Users/soutaro/.rbenv/versions/3.3.6/bin/irb:25:in `<top (required)>'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/cli/exec.rb:58:in `load'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/cli/exec.rb:58:in `kernel_load'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/cli/exec.rb:23:in `run'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/cli.rb:455:in `exec'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/vendor/thor/lib/thor/command.rb:28:in `run'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/vendor/thor/lib/thor.rb:527:in `dispatch'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/cli.rb:35:in `dispatch'
	from /Users/soutaro/.rbenv/versions/3.3.6/lib/ruby/gems/3.3.0/gems/bundler-2.5.16/lib/bundler/vendor/thor/lib/thor/base.rb:584:in `start'
	... 6 levels...

I think it's a bug of rubygems (or bundler)...