Warning due to missing `frozen_string_literal` magic comment with Ruby 3.4

[yui-har]

It worked fine in Ruby 3.3 (3.3.6) and earlier, but when I ran the tests in Ruby 3.4 (3.4.5) I got a warning.

# bundle exec rake test
Run options: --seed 48690

# Running:

/usr/local/bundle/gems/parseconfig-1.1.2/lib/parseconfig.rb:61: warning: literal string will be frozen in the future (run with --debug-frozen-string-literal for more information)
/usr/local/bundle/gems/parseconfig-1.1.2/lib/parseconfig.rb:61: warning: literal string will be frozen in the future (run with --debug-frozen-string-literal for more information)
... warnings displayed repeat ...

.

Finished in 19.547526s, 16.2169 runs/s, 77.6569 assertions/s.
317 runs, 1518 assertions, 0 failures, 0 errors, 0 skips

After confirm the following, I found that if a destructive operation is performed without a magic comment, a warning will be displayed.
https://github.com/ruby/ruby/releases/tag/v3_4_0
https://bugs.ruby-lang.org/issues/20205

The parseconfig gem is very useful, so it would be great if you could fix this.