`can't modify frozen String` error

[parthshyara]

The comment # frozen_string_literal: true was added in a recent commit that leads to the following error in the CI.

can't modify frozen String: "## Updated on 2023-02-13 07:47:24 +0000 by apt-spy2\n"

#91 fixes the issue.

[parthshyara]

@till Please review this. We are still unable to use this tool in the CI because of the mentioned issue.

[till]

Thanks again!