fix: warn when preload fails

[dummdidumm]

closes #8301
closes #8476

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[eltigerchino]

Should the warning use the term preloading instead of prefetching? Typing preload into the docs shows the relevant topics, whereas prefetch does not.

[Rich-Harris]

Should the warning use the term preloading instead of prefetching?

yeah, good catch — updated the text