[Fix #12082] Fix an error for Lint/UselessAssignment

Fixes #12082.

This PR fixes an error for `Lint/UselessAssignment` when a variable is assigned
and unreferenced in `for` with multiple variables.

Author: koic

changelog/fix_an_error_for_lint_useless_assignment.md

@@ -0,0 +1 @@
+* [#12082](https://github.com/rubocop/rubocop/issues/12082): Fix an error for `Lint/UselessAssignment` when a variable is assigned and unreferenced in `for` with multiple variables. ([@koic][])

lib/rubocop/cop/variable_force/assignment.rb

@@ -119,9 +119,7 @@ def rest_assignment_node
         end
 
         def for_assignment_node
-          return nil unless node.parent&.for_type?
-
-          node.parent
+          node.ancestors.find(&:for_type?)
         end
 
         def find_multiple_assignment_node(grandparent_node)

spec/rubocop/cop/lint/useless_assignment_spec.rb

@@ -270,6 +270,23 @@ module x::Foo
     end
   end
 
+  context 'when a variable is assigned and unreferenced in `for` with multiple variables' do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        for i, j in items
+               ^ Useless assignment to variable - `j`.
+          do_something(i)
+        end
+      RUBY
+
+      expect_correction(<<~RUBY)
+        for i, _ in items
+          do_something(i)
+        end
+      RUBY
+    end
+  end
+
   context 'when a variable is assigned and referenced in `for`' do
     it 'does not register an offense' do
       expect_no_offenses(<<~RUBY)