Fix StructUtilsSpec call to toByteArray #2271

Job	Run time
conformance	1m 40s
build (2_12, mima)	1m 31s
build (2_12, e2e)	3m 32s
build (2_12, test)	12m 3s
build (2_13, mima)	1m 8s
build (2_13, e2e)	4m 3s
build (2_13, test)	15m 39s
build (3, mima)	6s
build (3, e2e)	4m 32s
build (3, test)	14m 39s
build (2_12, examples_and_formatting)	2m 30s
build (2_13, scala3_compat_test)	9m 45s
build (3, scala3_compat_test)	8m 40s
ci-passed	1s
	1h 19m 49s

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