Use `clone_from()` in two places #797

Job	Run time
cross_test (stable, powerpc-unknown-linux-gnu)	37m 3s
clippy (beta)	2m 34s
tests (stable)	6m 23s
cross_test (stable, i686-unknown-linux-gnu)	5m 29s
tests (beta)	6m 50s
tests (nightly)	6m 53s
tests (1.51.0)	11m 54s
	1h 17m 6s

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