[Fix #9681] Fix an incorrect auto-correct for Style/RedundantBegin

Fixes #9681.

This PR fixes an incorrect auto-correct for `Style/RedundantBegin`
when using modifier `if` single statement in `begin` block.

changelog/fix_incorrect_autocorrect_for_style_redundant_begin.md

@@ -0,0 +1 @@
+* [#9681](https://github.com/rubocop/rubocop/issues/9681): Fix an incorrect auto-correct for `Style/RedundantBegin` when using modifier `if` single statement in `begin` block. ([@koic][])

lib/rubocop/cop/style/redundant_begin.rb

@@ -109,7 +109,10 @@ def register_offense(node)
         def replace_begin_with_statement(corrector, offense_range, node)
           first_child = node.children.first
 
-          corrector.replace(offense_range, first_child.source)
+          source = first_child.source
+          source = "(#{source})" if first_child.if_type?
+
+          corrector.replace(offense_range, source)
           corrector.remove(range_between(offense_range.end_pos, first_child.source_range.end_pos))
 
           restore_removed_comments(corrector, offense_range, node, first_child)

spec/rubocop/cop/style/redundant_begin_spec.rb

@@ -234,6 +234,20 @@ def method
     RUBY
   end
 
+  it 'registers and corrects an offense when using modifier `if` single statement in `begin` block' do
+    expect_offense(<<~RUBY)
+      var ||= begin
+              ^^^^^ Redundant `begin` block detected.
+        foo if condition
+      end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      var ||= (foo if condition)
+
+    RUBY
+  end
+
   it 'does not register an offense when using `begin` with multiple statement for or assignment' do
     expect_no_offenses(<<~RUBY)
       var ||= begin