autopkgtest failures due to removal of 3-arg Regexp::new in Ruby 3.3

[Pushkar Kulkarni]

docdiff autopkgtests fail with ruby-defaults 1:3.3~ubuntu3 [1]

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776s /usr/lib/ruby/vendor_ruby/docdiff/view.rb:95:in `initialize': wrong number of arguments (given 3, expected 1..2) (ArgumentError)
776s from /usr/lib/ruby/vendor_ruby/docdiff/view.rb:95:in `new'
776s from /usr/lib/ruby/vendor_ruby/docdiff/view.rb:95:in `apply_style_digest'
776s from /usr/lib/ruby/vendor_ruby/docdiff/view.rb:419:in `to_wdiff_digest'
776s from /usr/lib/ruby/vendor_ruby/doc_diff.rb:139:in `run'
776s from /usr/bin/docdiff:172:in `<main>'
776s autopkgtest [14:12:23]: test wdiff-digest: -----------------------]

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This seems to be a consequence of the removal of the 3-argument Regexp.new. See [2][3].

[1] https://objectstorage.prodstack5.canonical.com/swift/v1/AUTH_0f9aae918d5b4744bf7b827671c86842/autopkgtest-oracular/oracular/amd64/d/docdiff/20240820_141236_7a9ec@/log.gz
[2] https://bugs.ruby-lang.org/issues/18797
[3] https://www.ruby-lang.org/en/news/2023/12/25/ruby-3-3-0-released/