chore: use 5.2.0 for tests #27458

Job	Run time
Nix (macos-latest)	3m 58s
Nix (ubuntu-latest)	6m 21s
Coq 8.16.1	1m 23s
Coverage (5.2.x)	10m 2s
Build (macos-latest, 5.2.x)	16m 13s
Create local opam switch (macos-latest, 5)	6m 2s
Build (ubuntu-latest, 5.2.x)	9m 50s
MSVC 4.14.0 / windows_x86	10m 23s
Create local opam switch (macos-latest, 4.14)	5m 31s
Build (windows-latest, 5.2.x)	17m 17s
Documentation	43s
Create local opam switch (ubuntu-latest, 5)	4m 55s
MSVC 4.14.0 / windows_x86_64	10m 10s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	1m 57s
Create local opam switch (ubuntu-latest, 4.14)	4m 51s
Build (5.2.x, macos-13, true)	5m 19s
Format	8m 51s
Build (4.13.x, ubuntu-latest, true)	2m 3s
Build monorepo benchmark docker image	10m 8s
Build (4.08.x, ubuntu-latest, true)	1m 55s
Build (4.04.x, ubuntu-latest, true, true)	5m 24s
Build (4.02.x, ubuntu-latest, true)	4m 27s
	2h 27m 43s

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