Fix clippy lints #558

Job	Run time
Miri	1m 47s
benchmarks	1m 32s
clippy	54s
documentation	1m 20s
Optional features (approx selected)	33s
Optional features (none selected)	30s
rustfmt	13s
static SuiteSparse (stable, ubuntu-20.04, stable)	42s
test (msrv, ubuntu-20.04, 1.64.0)	2m 16s
test (stable, ubuntu-20.04, stable)	58s
static SuiteSparse (macos, macos-latest, stable)	1m 47s
test (beta, ubuntu-20.04, beta)	59s
static SuiteSparse (win-msvc, windows-2019, stable)	1m 21s
test (nightly, ubuntu-20.04, nightly)	1m 9s
static SuiteSparse (win-gnu, windows-2019, stable)	1m 15s
test (macos, macos-latest, stable)	2m 3s
test (win-msvc, windows-2019, stable)	2m 38s
test (win-gnu, windows-2019, stable)	1m 55s
	23m 52s

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