Fix Taffy viewport node leaks #56907

Job	Run time
miri	2m 26s
ci	2m 26s
typos	10s
build (windows-latest)	2m 12s
toml	1m 55s
build (ubuntu-latest)	2m 24s
check-bevy-internal-imports	5s
build (macos-latest)	2m 23s
check-doc	2m 24s
check-missing-examples-in-docs	30s
run-examples-macos-metal	2m 23s
check-missing-features-in-docs	28s
markdownlint	1m 4s
check-compiles-no-std	1s
check-compiles	1s
build-wasm-atomics	1s
build-wasm	1s
msrv	1s
	20m 55s

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