Fix `Dir::symlink_metadata` of "/" on Linux. (#396) #1799

Job	Run time
Check Cross-Compilation (stable)	2m 17s
Check Cross-Compilation (beta)	2m 38s
Check Cross-Compilation on Windows (stable)	4m 21s
Rustfmt	8s
Check Cross-Compilation on Windows (beta)	2m 20s
Check Cross-Compilation on Rust nightly (nightly)	3m 5s
Test linux-raw support (ubuntu-22.04)	39s
Fuzz Targets	45s
Test linux-raw support (ubuntu)	38s
Check Cross-Compilation on Rust nightly on Windows (nightly)	3m 16s
Test with Rust nightly (ubuntu)	37s
Test (stable)	36s
Test on Musl (ubuntu)	2m 32s
Test (aarch64-ubuntu)	4m 15s
Test (windows-2022)	2m 48s
Test (windows-latest)	3m 54s
Test (beta)	35s
Test (macos-13)	1m 30s
Test with Rust nightly (windows)	2m 4s
Test (ubuntu-22.04)	37s
Test (macos-latest)	37s
Test (msrv)	4m 48s
	45m 0s

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