Fix warning about hidden elided lifetime in `Drain` #250

Job	Run time
miri	44s
nostd/thumbv6m-none-eabi/stable	16s
tests (beta, serde, false)	22s
tests (stable, true, false)	37s
tests (1.51.0, serde, false, --skip spare_capacity_mut)	2m 6s
tests (1.70.0, serde, false)	29s
tests (nightly, serde, borsh, zeroize, false)	24s
	4m 58s

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