Failure to build docs of odoc.2.0.0 with odoc.3.0.0

[jonludlam]

We get a backtrace from odoc:

odoc: internal error, uncaught exception:
      File "src/html/link.ml", line 101, characters 16-22: Assertion failed
      Raised at Odoc_html__Link.href in file "src/html/link.ml", line 101, characters 16-57
      Called from Odoc_html__Generator.internallink in file "src/html/generator.ml", line 108, characters 19-49

pointing at https://github.com/ocaml/odoc/blob/42190737339d9be4510eeeb0e3c47e84badf4d73/src/html/link.ml#L101

Here are some logs (though they might get GC'd at some point): https://sage.caelum.ci.dev/job/2025-05-17/065324-voodoo-do-e3dc0a