[Fix #9613] Fix a false positive for Style/RedundantSelf

Fixes #9613.

This PR fixes a false positive for `Style/RedundantSelf`
when a self receiver on an lvalue of mlhs arguments.

changelog/fix_false_positive_for_style_redundant_self_cop.md

@@ -0,0 +1 @@
+* [#9613](https://github.com/rubocop/rubocop/issues/9613): Fix a false positive for `Style/RedundantSelf` when a self receiver on an lvalue of mlhs arguments. ([@koic][])

lib/rubocop/cop/style/redundant_self.rb

@@ -144,8 +144,12 @@ def regular_method_call?(node)
         end
 
         def on_argument(node)
-          name, = *node
-          @local_variables_scopes[node] << name
+          if node.mlhs_type?
+            on_args(node)
+          else
+            name, = *node
+            @local_variables_scopes[node] << name
+          end
         end
 
         def allow_self(node)

spec/rubocop/cop/style/redundant_self_spec.rb

@@ -234,4 +234,13 @@ def self.requested_specs
   it 'accepts a self receiver of methods also defined on `Kernel`' do
     expect_no_offenses('self.open')
   end
+
+  it 'accepts a self receiver on an lvalue of mlhs arguments' do
+    expect_no_offenses(<<~RUBY)
+      def do_something((a, b)) # This method expects Array that has 2 elements as argument.
+        self.a = a
+        self.b.some_method_call b
+      end
+    RUBY
+  end
 end