Clarify inconsistent GltfConvertCoordinates 0.18 behavior #72205

Job	Run time
toml	7s
ci	5m 29s
typos	8s
check-release-content	27s
build (windows-latest)	20m 38s
check-bevy-internal-imports	7s
build (ubuntu-latest)	11m 32s
miri	19m 52s
check-doc	10m 25s
build (macos-latest)	11m 43s
check-missing-examples-in-docs	34s
check-missing-features-in-docs	46s
markdownlint	1m 25s
check-compiles-no-std-portable-atomic	1m 16s
check-compiles-no-std-examples	1m 5s
check-compiles-no-std	1m 47s
check-compiles	8m 29s
build-wasm-atomics	1m 45s
msrv	2m 22s
build-wasm	1m 43s
	1h 41m 40s

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