Normalise warnings messages

[johnnovak]

Description

I've just done a warning message normalisations sweep for consistency. I like consistency, as you can tell 😎

I left the viewport_resolution related warnings intentionally alone as I'm addressing those in my upcoming PR.

Manual testing

DOSBox still compiles & starts up 😄 (no functional changes)

Checklist

Please tick the items as you have addressed them. Don't remove items; leave the ones that are not applicable unchecked.

I have:

• followed the project's contributing guidelines and code of conduct.
• performed a self-review of my code.
• commented on the particularly hard-to-understand areas of my code.
• split my work into well-defined, bisectable commits, and I named my commits well.
• applied the appropriate labels (bug, enhancement, refactoring, documentation, etc.)
• checked that all my commits can be built.
• confirmed that my code does not cause performance regressions (e.g., by running the Quake benchmark).
• added unit tests where applicable to prove the correctness of my code and to avoid future regressions.
• made corresponding changes to the documentation or the website according to the documentation guidelines.
• locally verified my website or documentation changes.

[weirddan455]

Just one minor wording suggestion