Fix Ruby 2.7 CI failure by conditionally requiring stdlib gems

The uri, json, and logger gems are default gems in Ruby 2.7-3.3 and
cannot be overridden. Only add them as explicit dependencies for
Ruby 3.4+ where they're being extracted from stdlib.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: geetfun

checkend-ruby.gemspec

@@ -27,8 +27,11 @@ Gem::Specification.new do |spec|
 
   spec.require_paths = ['lib']
 
-  # Ruby stdlib gems that are being extracted (future-proofing for Ruby 3.5+)
-  spec.add_dependency 'json'
-  spec.add_dependency 'logger'
-  spec.add_dependency 'uri'
+  # Ruby stdlib gems being extracted in Ruby 3.4+/3.5+
+  # Only add as dependencies for Ruby versions where they're no longer bundled
+  if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('3.4')
+    spec.add_dependency 'json'
+    spec.add_dependency 'logger'
+    spec.add_dependency 'uri'
+  end
 end