t7800: work around the MSYS path conversion on Windows #2088

Job	Run time
config	9s
fuzz smoke test	1m 19s
win+VS build	0s
win build	5m 0s
win+Meson build	3m 34s
osx-reftable (macos-14)	18m 21s
osx-gcc (macos-14)	17m 43s
osx-clang (macos-14)	18m 4s
documentation	7m 18s
osx-meson (macos-14)	21m 23s
static-analysis	5m 44s
rust-analysis	1m 33s
linux-musl-meson (alpine:latest)	8m 8s
sparse	3m 22s
linux-sha256 (ubuntu:rolling)	13m 20s
linux-reftable-leaks (ubuntu:rolling)	35m 6s
linux-asan-ubsan (ubuntu:rolling)	34m 33s
linux-leaks (ubuntu:rolling)	34m 2s
linux32 (i386/ubuntu:focal)	10m 43s
linux-meson (ubuntu:rolling)	14m 6s
debian-11 (debian:11)	10m 25s
almalinux-8 (almalinux:8)	9m 40s
linux-breaking-changes (ubuntu:rolling)	10m 29s
linux-reftable (ubuntu:rolling)	13m 29s
linux-TEST-vars (ubuntu:20.04)	13m 3s
fedora-breaking-changes-meson (fedora:latest)	9m 51s
win+VS test	-1s
win+Meson test (1)	8m 3s
win+Meson test (0)	11m 13s
win+Meson test (5)	14m 56s
win+Meson test (4)	10m 30s
win+Meson test (7)	8m 6s
win+Meson test (8)	8m 17s
win+Meson test (9)	9m 0s
win+Meson test (3)	11m 2s
win+Meson test (2)	11m 32s
win+Meson test (6)	9m 3s
win test (6)	8m 23s
win test (3)	4m 54s
win test (7)	6m 48s
win test (8)	10m 24s
win test (9)	6m 58s
win test (0)	7m 37s
win test (1)	8m 9s
win test (4)	10m 18s
win test (2)	9m 2s
win test (5)	8m 31s
	8h 23m 10s

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