Add -r logger to validate task for rbs library

Because `logger` was removed from manifest.yaml, the validate task
needs to explicitly load the logger library when validating rbs
signatures, as sig/rbs.rbs references ::Logger.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: soutaro

Rakefile

@@ -203,8 +203,8 @@ task :validate => :compile do
     args = ["-r", lib]
 
     if lib == "rbs"
-      args << "-r"
-      args << "prism"
+      args << "-r" << "prism"
+      args << "-r" << "logger"
     end
 
     sh "#{ruby} #{rbs} #{args.join(' ')} validate"