pinned opam package with git submodules fail to install on windows.

[hhugo]

There might be an issue when installing a pinned package that contain a git submodule on windows.

See https://github.com/ocsigen/js_of_ocaml/actions/runs/9467891659/job/26082990039

[WARNING] Warning: cannot copy D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\sources\js_of_ocaml-compiler\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete\method-delete-twice-covered-err-delete-member-expression-private-method-async-gen.js to D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\build\js_of_ocaml-compiler.dev\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete
[WARNING] Warning: cannot copy D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\sources\js_of_ocaml-compiler\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete\method-delete-twice-covered-err-delete-member-expression-private-method-accessor-set.js to D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\build\js_of_ocaml-compiler.dev\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete
[WARNING] Warning: cannot copy D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\sources\js_of_ocaml-compiler\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete\method-delete-twice-covered-err-delete-member-expression-private-method-accessor-get.js to D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\build\js_of_ocaml-compiler.dev\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete

#=== ERROR while compiling js_of_ocaml-compiler.dev ===========================#
Cannot copy D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\sources\js_of_ocaml-compiler\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete\method-delete-twice-covered-err-delete-call-expression-private-method-async-gen.js to D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\build\js_of_ocaml-compiler.dev\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete\method-delete-twice-covered-err-delete-call-expression-private-method-async-gen.js (C:\hostedtoolcache\windows\opam\2.2.0-beta3\x86_64\opam.exe: "open" failed on D:\a\js_of_ocaml\js_of_ocaml\_opam\.opam-switch\build\js_of_ocaml-compiler.dev\compiler\tests-js-parser\test262\test\language\statements\class\elements\syntax\early-errors\delete\method-delete-twice-covered-err-delete-call-expression-private-method-async-gen.js: No such file or directory).

[dra27]

Just to note that this is blowing the MAX_PATH limit.