CI: faster with borg-dir/borg.exe, fixes #9236 #5365

Job	Run time
security	14s
lint	7s
native_tests (ubuntu-22.04, 3.10, py310-llfuse)	11m 22s
native_tests (ubuntu-24.04, 3.14, py314-mfusepy)	15m 43s
vm_tests (haiku, r1beta5, Haiku, false)	13m 45s
vm_tests (openbsd, 7.7, OpenBSD, false)	20m 8s
vm_tests (freebsd, 14.3, FreeBSD, true, borg-freebsd-14-x86_64-gh)	21m 41s
native_tests (ubuntu-22.04, 3.11, docs)	3m 0s
native_tests (ubuntu-22.04, 3.10, mypy)	3m 31s
vm_tests (netbsd, 10.1, NetBSD, false)	16m 19s
asan_ubsan	6m 4s
windows_tests	0s
	1h 51m 54s

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