Fix interpretation of 'exists_if' in META files #27035

Job	Run time
Coverage (4.14.x)	11m 28s
Coq 8.16.1	8m 52s
Create local opam switch (macos-latest, 5)	9m 31s
Build (macos-latest, 4.14.x)	16m 31s
Create local opam switch (macos-latest, 4.14)	6m 4s
Build (ubuntu-latest, 4.14.x)	12m 33s
MSVC 4.14.0 / windows_x86	10m 36s
Create local opam switch (ubuntu-latest, 5)	6m 9s
Documentation	36s
Build (windows-latest, 4.14.x)	6m 56s
MSVC 4.14.0 / windows_x86_64	10m 36s
Create local opam switch (ubuntu-latest, 4.14)	5m 29s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	2m 22s
Build (5.1.x, ubuntu-latest, true)	2m 22s
Format	2m 29s
Build monorepo benchmark docker image	3m 55s
Nix (macos-latest)	4m 41s
Build (5.1.x, macos-latest, true)	2m 49s
Nix (ubuntu-latest)	1m 0s
Build (4.14.x, macos-13, true)	5m 14s
Build (4.13.x, ubuntu-latest, true)	2m 36s
Build (4.08.x, ubuntu-latest, true)	2m 31s
Build (4.04.x, ubuntu-latest, true, true)	5m 35s
Build (4.02.x, ubuntu-latest, true)	4m 49s
	2h 25m 44s

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