Fix Taffy viewport node leaks #56906

Job	Run time
build (windows-latest)	11m 5s
ci	2m 52s
miri	11m 24s
toml	2m 0s
build (ubuntu-latest)	6m 16s
check-bevy-internal-imports	7s
check-doc	10m 34s
check-missing-examples-in-docs	34s
build (macos-latest)	5m 39s
run-examples-macos-metal	8m 25s
typos	14s
check-missing-features-in-docs	28s
markdownlint	1m 2s
check-compiles	5m 42s
check-compiles-no-std	1m 45s
build-wasm-atomics	1s
build-wasm	1s
msrv	1s
	1h 8m 10s

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