Update transfer.py with as_posix paths #1471

Job	Run time
sdist_verify	13s
docs / Load tox environments	4s
allowed-fail-tests / Load tox environments	6s
tests / Load tox environments	6s
docs / build_docs-notebooks (ubuntu-latest)	4m 58s
tests / py312 (ubuntu-latest)	4m 36s
tests / py311 (ubuntu-latest)	3m 47s
tests / py311-online (windows-latest)	5m 33s
tests / py310 (macos-latest)	5m 1s
tests / py310-oldestdeps (ubuntu-latest)	3m 21s
allowed-fail-tests / py311-devdeps (ubuntu-latest)	56m 4s
publish	0s
notify	0s
	1h 23m 49s

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