Fix a false positive for Style/CollectionCompact

This PR fixes a false positive for `Style/CollectionCompact` when using `reject`
on hash to reject nils in Ruby 2.3 analysis.
Because `Hash#compact` and `Hash#compact!` have been introduced in Ruby 2.4.

changelog/fix_a_false_positive_for_style_collection_compact.md

@@ -0,0 +1 @@
+* [#11799](https://github.com/rubocop/rubocop/pull/11799): Fix a false positive for `Style/CollectionCompact` when using `reject` on hash to reject nils in Ruby 2.3 analysis. ([@koic][])

lib/rubocop/cop/style/collection_compact.rb

@@ -36,11 +36,14 @@ module Style
       class CollectionCompact < Base
         include RangeHelp
         extend AutoCorrector
+        extend TargetRubyVersion
 
         MSG = 'Use `%<good>s` instead of `%<bad>s`.'
         RESTRICT_ON_SEND = %i[reject reject! select select!].freeze
         TO_ENUM_METHODS = %i[to_enum lazy].freeze
 
+        minimum_target_ruby_version 2.4
+
         # @!method reject_method_with_block_pass?(node)
         def_node_matcher :reject_method_with_block_pass?, <<~PATTERN
           (send !nil? {:reject :reject!}

spec/rubocop/cop/style/collection_compact_spec.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-RSpec.describe RuboCop::Cop::Style::CollectionCompact, :config do
+RSpec.describe RuboCop::Cop::Style::CollectionCompact, :config, :ruby24 do
   it 'registers an offense and corrects when using `reject` on array to reject nils' do
     expect_offense(<<~RUBY)
       array.reject { |e| e.nil? }
@@ -157,4 +157,13 @@ def foo(params)
       RUBY
     end
   end
+
+  context 'when Ruby <= 2.3', :ruby23 do
+    it 'does not register an offense when using `reject` on hash to reject nils' do
+      expect_no_offenses(<<~RUBY)
+        hash.reject { |k, v| v.nil? }
+        hash.reject! { |k, v| v.nil? }
+      RUBY
+    end
+  end
 end