docs/vale-styles: Bump all style violations to "error" level so they fail CI

[issyl0]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
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• Have you successfully run brew man locally and committed any changes?

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• I added these all the way back in December 2019 in Add Vale linting for our docs #6826, but only today (thanks to my Sorbet PR) realised that things have been failing unnoticeably because "warning" level exits with status code 0, so doesn't fail CI.
• Upgrading to "error" level will enable us to see the style errors in our docs in every CI run and fix them faster.
• My editor also auto-formatted the YAML to have double quotes instead of single. And I fixed all the remaining style failures, now I can see them!

[issyl0]

I've attempted an upstream PR to fix (hopefully) the errors we're seeing with not being able to use / in capitalization exclusions any more.

On the upside, at least these "style failures" fail the CI build now!

[Rylan12]

Good catch! Should the rules for oxford commas and pronouns be upgraded to errors as well?

[MikeMcQuaid]

Thanks @issyl0!

Good catch! Should the rules for oxford commas and pronouns be upgraded to errors as well?

Agreed. I don't personally see the point in any non-error rules as they will be ignored and the warnings be confusing when an actual error occurs.

[issyl0]

Should the rules for oxford commas and pronouns be upgraded to errors as well?

Good catch, that was an oversight rather than a deliberate choice. Done now, everything is at "error" level.