add missing mention of sort_unstable_by_key in QuerySortedIter docs #44648

Job	Run time
build (windows-latest)	5m 30s
build (ubuntu-latest)	2m 18s
check-bevy-internal-imports	4s
check-cfg	2m 0s
build (macos-latest)	2m 1s
check-doc	8m 43s
check-missing-examples-in-docs	28s
ci	2m 29s
miri	7m 22s
run-examples-macos-metal	6m 8s
toml	1m 47s
typos	9s
check-missing-features-in-docs	36s
markdownlint	1m 8s
check-compiles	4m 15s
build-wasm-atomics	1m 22s
build-wasm	1m 11s
msrv	55s
	48m 26s

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