Fix an error for `Layout/BlockAlignment` when using Ruby 3.1.0-dev ยท rubocop/rubocop@1c9abe9

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 `sta...