Tests

Add WeightedIndex::update_weights_relative #708

Job	Run time
test-cross (ubuntu-latest, powerpc-unknown-linux-gnu, stable)	1m 28s
test-miri	2m 15s
Check doc	1m 9s
test-ios	23s
test (ubuntu-latest, x86_64-unknown-linux-gnu, stable)	55s
test-no-std	14s
test (macos-latest, x86_64-apple-darwin, stable)	1m 18s
test (windows-latest, x86_64-pc-windows-gnu, stable)	2m 8s
test (windows-latest, x86_64-pc-windows-msvc, beta)	1m 53s
test (ubuntu-latest, x86_64-unknown-linux-gnu, MSRV, 1.60.0)	4m 38s
test (ubuntu-latest, sudo apt-get update ; sudo apt install gcc-multilib, i686-unknown-linux-gnu,...	1m 44s
test (ubuntu-latest, x86_64-unknown-linux-gnu, nightly, minimal_versions)	35s
	18m 40s

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