fix backslashes in path used for `asm_tests` #2489

Job	Run time
build (gcc-15.deb, --std-tests)	5m 52s
build (gcc-15.deb, --test-libcore)	14m 5s
build (gcc-15.deb, --extended-rand-tests)	8m 26s
build (gcc-15.deb, --extended-regex-example-tests)	6m 30s
build (gcc-15.deb, --extended-regex-tests)	11m 24s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	12m 5s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	11m 23s
build (gcc-15.deb, --projects)	11m 36s
build (gcc-15-without-int128.deb, --std-tests)	6m 0s
build (gcc-15-without-int128.deb, --test-libcore)	14m 26s
build (gcc-15-without-int128.deb, --extended-rand-tests)	8m 23s
build (gcc-15-without-int128.deb, --extended-regex-example-tests)	6m 26s
build (gcc-15-without-int128.deb, --extended-regex-tests)	11m 35s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	11m 39s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	11m 27s
build (gcc-15-without-int128.deb, --projects)	11m 23s
build_system	26s
duplicates	4s
success	1s
	2h 43m 11s

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