[ruby/securerandom] Random::Formatter is only provided from Ruby 3.1

ruby/securerandom@90c7e390f5

Author: hsbt

lib/securerandom.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |spec|
   spec.summary       = %q{Interface for secure random number generator.}
   spec.description   = %q{Interface for secure random number generator.}
   spec.homepage      = "https://github.com/ruby/securerandom"
-  spec.required_ruby_version = Gem::Requirement.new(">= 2.6.0")
+  spec.required_ruby_version = Gem::Requirement.new(">= 3.1.0")
   spec.licenses      = ["Ruby", "BSD-2-Clause"]
 
   spec.metadata["homepage_uri"] = spec.homepage