Fix cram tests build-path-prefix-map substitutions #29719

Job	Run time
Build microbenchmarks	2m 34s
Create local opam switch (macos-latest, 5)	6m 0s
Coq 8.16.1	7m 5s
Build (macos-latest, 5.1.x)	13m 44s
Create local opam switch (macos-latest, 4.14)	6m 18s
Build (ubuntu-latest, 5.1.x)	8m 38s
Documentation	53s
Create local opam switch (ubuntu-latest, 5)	4m 54s
Format	1m 4s
Build (ocaml-variants.5.4.0+trunk, ubuntu-latest, true)	1m 29s
Create local opam switch (ubuntu-latest, 4.14)	4m 52s
Build (4.14.x, ubuntu-latest, true)	1m 31s
Build monorepo benchmark docker image	3m 41s
Nix (macos-latest)	2m 6s
Build (4.14.x, macos-latest, true)	3m 22s
Wasm_of_ocaml	10m 37s
Nix (ubuntu-latest)	51s
Build (5.1.x, macos-13, true)	4m 15s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	14m 22s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 34s
Build (4.08.x, ubuntu-latest, true)	1m 34s
Build (4.04.x, ubuntu-latest, true, true)	4m 45s
Build (4.02.x, ubuntu-latest, true)	3m 56s
	1h 57m 5s

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