wp_die() updates for the Themes component

[CallumBW95]

Update wp_die() to include status codes where appropriate within files related to the Themes component

Trac ticket: #64057

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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Props callumbw95, mindctrl. 

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[github-actions]

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[mindctrl]

@CallumBW95 looks good. The failed checks appear to be related to a GitHub outage on macOS builds.

https://www.githubstatus.com/

[CallumBW95]

@mindctrl Ah ok, is there anyway I can rerun the tests as it looks like there are no issues with MacOS runners now?

[mindctrl]

@CallumBW95 AFAIK the only way, without extra permissions to this repo, is to push another commit.