Fix `Dir::symlink_metadata` of "/" on Linux. #1795

Job	Run time
Test with Rust nightly (ubuntu)	39s
Test with Rust nightly (windows)	1m 12s
Test on Musl (ubuntu)	2m 40s
Rustfmt	9s
Test linux-raw support (ubuntu)	38s
Check Cross-Compilation on Windows (stable)	1m 16s
Check Cross-Compilation on Windows (beta)	1m 23s
Test linux-raw support (ubuntu-22.04)	39s
Check Cross-Compilation (beta)	2m 2s
Check Cross-Compilation (stable)	2m 3s
Test (msrv)	4m 13s
Check Cross-Compilation on Rust nightly (nightly)	2m 47s
Check Cross-Compilation on Rust nightly on Windows (nightly)	1m 15s
Test (macos-13)	1m 20s
Test (windows-latest)	1m 47s
Test (windows-2022)	1m 15s
Test (stable)	37s
Test (macos-latest)	1m 11s
Test (ubuntu-22.04)	53s
Test (aarch64-ubuntu)	1m 22s
Test (beta)	36s
Fuzz Targets	52s
	30m 49s

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