Update smol_str requirement from 0.2 to 0.3 #58108

Job	Run time
build (windows-latest)	1m 59s
ci	2m 32s
build (ubuntu-latest)	2m 0s
build (macos-latest)	2m 19s
check-bevy-internal-imports	4s
check-doc	2m 21s
check-missing-examples-in-docs	26s
miri	13m 30s
run-examples-macos-metal	2m 47s
toml	1m 52s
typos	6s
check-missing-features-in-docs	27s
markdownlint	1m 4s
msrv	0s
build-wasm	0s
build-wasm-atomics	0s
check-compiles-no-std	0s
check-compiles	0s
	31m 27s

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