[ruby/pp] Drop to support < Ruby 2.7

https://github.com/ruby/pp/commit/e92228964b

lib/pp.gemspec

@@ -7,9 +7,10 @@ Gem::Specification.new do |spec|
   spec.summary       = %q{Provides a PrettyPrinter for Ruby objects}
   spec.description   = %q{Provides a PrettyPrinter for Ruby objects}
   spec.homepage      = "https://github.com/ruby/pp"
-  spec.required_ruby_version = Gem::Requirement.new(">= 2.3.0")
   spec.licenses      = ["Ruby", "BSD-2-Clause"]
 
+  spec.required_ruby_version = Gem::Requirement.new(">= 2.7.0")
+
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = spec.homepage