Improve shader_material example #32198

Job	Run time
check-bevy-internal-imports	3s
build (windows-latest)	4m 10s
check-doc	5m 22s
check-missing-examples-in-docs	33s
build (ubuntu-latest)	1m 43s
ci	1m 30s
build (macos-latest)	2m 56s
miri	8m 11s
run-examples-on-windows-dx12	17m 36s
check-missing-features-in-docs	30s
markdownlint	1m 12s
check-compiles	2m 25s
msrv	1m 16s
build-wasm	48s
	48m 15s

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