Stackoverflow in src/solver/solver.ml when running solve without cache.

[tmcgilchrist]

This seems to only appear on docs.ci.ocaml.org, which makes sense because it is handling the entire opam-repository set of packages as compared to staging which only builds the latest version of each package.

infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Dune__exe__Solver.universes.aux in file "src/solver/solver.ml", line 48, characters 10-294
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Dune__exe__Solver.universes.aux.(fun) in file "src/solver/solver.ml", line 53, characters 62-71
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Stdlib__List.rev_map.rmap_f in file "list.ml", line 103, characters 22-25
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Dune__exe__Solver.universes.aux in file "src/solver/solver.ml", line 48, characters 10-294
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Dune__exe__Solver.universes.aux.(fun) in file "src/solver/solver.ml", line 53, characters 62-71
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Stdlib__List.rev_map.rmap_f in file "list.ml", line 103, characters 22-25
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Dune__exe__Solver.universes.aux in file "src/solver/solver.ml", line 48, characters 10-294
infra_docs-ci.1.76qh2d0e8wgg@eumache    | Called from Dune__exe__Solver.universes.aux.(fun) in file "src/solver/solver.ml", line 53, characters 62-71