PBR: use attenuation instead of base_color for attenuation #37883

Job	Run time
build (windows-latest)	4m 9s
build (ubuntu-latest)	2m 15s
check-bevy-internal-imports	4s
build (macos-latest)	2m 18s
check-cfg	52s
check-doc	7m 17s
check-missing-examples-in-docs	29s
ci	2m 17s
miri	4m 54s
run-examples-macos-metal	4m 12s
toml	1m 58s
typos	7s
check-missing-features-in-docs	32s
markdownlint	1m 8s
check-compiles	2m 12s
build-wasm	32s
msrv	49s
	36m 5s

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