False negative for `Layout/LineLength` with split heredoc

[andyw8]

Expected behavior

Given this code, and max line length set to 120:

x = <<~FOO
  a \
  abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef abcdef
FOO

RuboCop should complain with Layout/LineLength: Line is too long. [127/120].

Actual behavior

RuboCop doesn't complain. But if I set ParserEngine: parser_prism, then it correctly reports the issue.

RuboCop version

Include the output of rubocop -V or bundle exec rubocop -V if using Bundler. If you see extension cop versions (e.g. rubocop-performance, rubocop-rspec, and others) output by rubocop -V, include them as well. Here's an example:

$ [bundle exec] rubocop -V
1.63.1 (using Parser 3.2.2.3, rubocop-ast 1.29.0, running on ruby 3.2.2) [x86_64-linux]
  - rubocop-performance 1.18.0
  - rubocop-rspec 2.23.2