Refactor URI host handling to ensure downcasing is applied correctly on frozen strings

[pedrol3001]

Overview

When passing a frozen string as the host, the agent breaks with the following error:

FrozenError (can't modify frozen String)

I encountered this issue while using the Pusher gem. The idea of this pull request is to replace the use of the downcase! method with a reassignment of the string, preventing errors when working with frozen strings.

I have applied thos changes on my project and it started to work fine.

Submitter Checklist:

• Include a link to the related GitHub issue, if applicable.
• Include a security review link, if applicable

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Reviewer Checklist

• Perform code review
• Add performance label
• Perform appropriate level of performance testing
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• Add version label prior to acceptance

[kaylareopelle]

Thanks, @pedrol3001! Good catch. This looks great!