fix: restore 4.08 compat (#11397) #29790

Job	Run time
Coq 8.16.1	7m 9s
Build microbenchmarks	2m 36s
Create local opam switch (macos-latest, 5)	5m 13s
Create local opam switch (macos-latest, 4.14)	5m 15s
Create local opam switch (ubuntu-latest, 5)	4m 45s
Documentation	52s
Format	1m 2s
Create local opam switch (ubuntu-latest, 4.14)	4m 51s
Build (macos-latest, 5.1.x)	12m 58s
Build monorepo benchmark docker image	3m 52s
Nix (macos-latest)	1m 51s
Build (ubuntu-latest, 5.1.x)	9m 3s
Wasm_of_ocaml	10m 13s
Build (ocaml-variants.5.4.0+trunk, ubuntu-latest, true)	1m 30s
Nix (ubuntu-latest)	52s
Build (4.14.x, ubuntu-latest, true)	1m 32s
Build (4.14.x, macos-latest, true)	2m 15s
Build (5.1.x, macos-13, true)	3m 58s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	14m 44s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	8m 14s
Build (4.08.x, ubuntu-latest, true)	1m 6s
Build (4.04.x, ubuntu-latest, true, true)	4m 40s
Build (4.02.x, ubuntu-latest, true)	3m 52s
	1h 52m 23s

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