refactor: missed lint message .to_string() change to .to_owned()

[hippietrail]

Issues

Continues on from what was missed in #3569

Description

Back in #3569 I thought I changed all the message fields of Lints that were using .to_string() to standardize on .to_owned() after looking into why both were used and finding reasons that .to_owned() was probably the better one after all, despite my using .to_string() in most of my linters.

Before searching the repo I expected only the skeleton linters were still using .to_string() but there was a lot I was missing!

How Has This Been Tested?

cargo test

AI Disclosure

• I am a human and didn't use any AI.
• I used LLM features of my editor, but not an agent.
• I used an AI agent interactively.
• I am an agent or I got an agent to do the work autonomously.

Checklist

• I have performed a self-review of my own code
• I have added tests to cover my changes
• I have considered splitting this into smaller pull requests.