Fix an error for Layout/BlockAlignment when using Ruby 3.1.0-dev

This PR fixes the following build error.

```console
% bundle exec rspec ./spec/rubocop/cop/layout/block_alignment_spec.rb:222
(snip)

      # ./lib/rubocop/cop/layout/block_alignment.rb:97:in `start_for_block_node'
      # ./lib/rubocop/cop/layout/block_alignment.rb:82:in `on_block'
      # ./lib/rubocop/cop/commissioner.rb:100:in `public_send'
      # ./lib/rubocop/cop/commissioner.rb:100:in `block (2 levels) in trigger_responding_cops'
      # ./lib/rubocop/cop/commissioner.rb:160:in `with_cop_error_handling'
      # ./lib/rubocop/cop/commissioner.rb:99:in `block in trigger_responding_cops'
```

https://app.circleci.com/pipelines/github/rubocop/rubocop/5414/workflows/4a7e4b81-7380-41e5-8ede-e28d9160010d/jobs/201236

I reported on this change of behavior.
https://bugs.ruby-lang.org/issues/18268

And it was due to the following change.
ruby/ruby#1509

This PR will be changed to the cop logic that is not affected by the above Ruby 3.1.0-dev change.

lib/rubocop/cop/layout/block_alignment.rb

@@ -101,11 +101,11 @@ def start_for_block_node(block_node)
         def block_end_align_target(node)
           lineage = [node, *node.ancestors]
 
-          target = lineage.each_cons(2) do |current, parent|
-            break current if end_align_target?(current, parent)
+          lineage.each_cons(2) do |current, parent|
+            return current if end_align_target?(current, parent)
           end
 
-          target || lineage.last
+          lineage.last
         end
 
         def end_align_target?(node, parent)