Can't build ocamlbuild on Windows: `Error: opendir(): No such file or directory`

[gridbugs]

Dune fails to build the ocamlbuild package on Windows. The error while building a project depending on ocamlbuild is:

> dune build
Error: opendir(): No such file or directory
-> required by
   _build/_fetch/checksum/sha512=9bf33e2e3cd70495c6ff5987f7e8c1c2fb3dccb02da490140726fed3b374489cb93d500f57bea32a1a71da1c9d3dd207e476109d1aaa759f54c3ef07d5b7ccd8/dir
-> required by _build/_private/default/.pkg/ocamlbuild/source
-> required by _build/_private/default/.pkg/ocamlbuild/target

Once the build has failed in this way, Dune is unable to clean the project:

> dune clean
Error:
rmdir(_build\_fetch\checksum\sha512=9bf33e2e3cd70495c6ff5987f7e8c1c2fb3dccb02da490140726fed3b374489cb93d500f57bea32a1a71da1c9d3dd207e476109d1aaa759f54c3ef07d5b7ccd8\dir\samples): Directory not empty

Repro case: https://github.com/gridbugs/dune-windows-repros/tree/main/repro4