Extract release notes lines to an array to later join it

[iangmaia]

Internal reference: p1744652620596379-slack-C06CKSPHYA1

What does it do?

There was an issue in the code due to the recent frozen_string_literal update and the fact that we're modifying with chomp! a String pre-initialized with an empty value.
I've updated the code a bit to extract the lines first to an array to later join + chomp it.

Checklist before requesting a review

• Run bundle exec rubocop to test for code style violations and recommendations.
• Add Unit Tests (aka specs/*_spec.rb) if applicable.
• Run bundle exec rspec to run the whole test suite and ensure all your tests pass.
• Make sure you added an entry in the CHANGELOG.md file to describe your changes under the appropriate existing ### subsection of the existing ## Trunk section.
• If applicable, add an entry in the MIGRATION.md file to describe how the changes will affect the migration from the previous major version and what the clients will need to change and consider.