cp: Fixed posixly correct dangling symlink test #17112

Job	Run time
Style/spelling (ubuntu-latest, feat_os_unix)	14s
Style/lint (windows-latest, feat_os_windows)	3m 18s
Style/format (ubuntu-latest, feat_os_unix)	19s
Pre-commit hooks	33s
Style/lint (ubuntu-latest, all, true)	2m 22s
Style/toml	13s
Style/Python	6s
Style/lint (macos-latest, feat_os_macos)	3m 27s
	10m 32s

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