Incremental repository loading loads every subdirectories including those not into packages/

[kit-ty-kate]

#6614 (part of opam 2.5.0) added incremental loading of repositories. However, unlike load_opams_from_dir, load_opams_from_diff does not look into the packages/ directory but starts from the repository root itself instead.

This means that adding a repository with /test.1/opam will not initially add a test.1 package, but subsequent updates will.

This bug is present in opam 2.5.0 only.