Tests

Add WeightedIndex::update_weights_relative #707

Job	Run time
test-ios	26s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	1m 4s
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	1m 40s
test (macos-latest, x86_64-apple-darwin, stable)	2m 37s
Check doc	1m 8s
test (windows-latest, x86_64-pc-windows-gnu, stable)	2m 28s
test-miri	2m 20s
test-no-std	15s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 54s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	5m 3s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	2m 47s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	32s
	22m 14s

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