Use inferred type for `useFetch`

Editor assessment

The subject is concrete about the mechanism and the beneficiary — `useFetch` now uses an inferred type — so the header communicates the improvement without the diff, and fix(nuxt3) classifies and locates it correctly. Hygiene is clean: imperative, unpunctuated end, reasonable length, no ticket junk. No body is present, acceptable for a small typing correction, though a phrase about the incorrect type developers saw would have deepened the example. No footer is required. Clear, accurate, and only minimally flawed: a good example.