tests: Tweak git_ls_files #2183

Job	Run time
miri	2m 32s
build (aarch64-unknown-linux-gnu)	2m 28s
test (stable)	3m 41s
build (aarch64-unknown-linux-musl)	2m 11s
test (beta)	4m 5s
build (aarch64-apple-darwin)	3m 7s
build (x86_64-unknown-linux-gnu)	1m 55s
test (nightly)	5m 2s
build (x86_64-unknown-linux-musl)	2m 9s
test (nightly, macos-11)	6m 9s
build (x86_64-apple-darwin)	2m 49s
test (nightly, windows-2019)	8m 45s
build (x86_64-pc-windows-msvc)	4m 53s
build (universal-apple-darwin)	3m 46s
deny / deny	19s
msrv / msrv	6m 35s
tidy / tidy	1m 20s
	1h 1m 46s

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