chore(nix): support build for experimental feature #28035

Job	Run time
Coq 8.16.1	8m 35s
Build microbenchmarks	5m 20s
Coverage (4.14.x)	9m 7s
Build (macos-latest, 4.14.x)	13m 33s
Build (ubuntu-latest, 4.14.x)	8m 33s
Create local opam switch (macos-latest, 5)	5m 35s
Documentation	1m 9s
Format	2m 39s
Create local opam switch (macos-latest, 4.14)	6m 48s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	4m 57s
Create local opam switch (ubuntu-latest, 5)	4m 58s
Build (5.1.x, ubuntu-latest, true)	1m 40s
Build monorepo benchmark docker image	1m 53s
Create local opam switch (ubuntu-latest, 4.14)	5m 5s
Nix (macos-latest)	39s
Build (5.1.x, macos-latest, true)	2m 57s
Nix (ubuntu-latest)	9s
Build (4.14.x, macos-13, true)	6m 28s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	10m 26s
Build (ocaml-base-compiler.4.14.2,system-mingw, windows-latest)	9m 47s
Build (4.13.x, ubuntu-latest, true)	1m 33s
Build (4.08.x, ubuntu-latest, true)	1m 36s
Build (4.04.x, ubuntu-latest, true, true)	4m 55s
Build (4.02.x, ubuntu-latest, true)	4m 16s
	2h 2m 38s

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