Update required Ruby version to >= 3.3

- Ruby 3.1 is EoL and blocking some dependency updates that have CVEs. So let's bump it to a not EoL but still pretty old version as the baseline.

Author: issyl0

rubocop-github.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |s|
 
   s.files = Dir["README.md", "STYLEGUIDE.md", "LICENSE", "config/*.yml", "lib/**/*.rb", "guides/*.md"]
 
-  s.required_ruby_version = ">= 3.1.0"
+  s.required_ruby_version = ">= 3.3.0"
 
   s.add_dependency "rubocop", ">= 1.76"
   s.add_dependency "rubocop-performance", ">= 1.24"