Local repositories containing git-lfs files can fail to be pinned in some cases

[kit-ty-kate]

Detected in ocaml/setup-ocaml#895

In the issue above, the actions/checkout action will shallow-clone the source repository by default and not initialize git-lfs leaving the lfs files bare.

Now there are several problems arising with this setup when using opam:

• opam pin add -n . will fail because it will try to use git-lfs. But git-lfs isn't setup so i'm a bit confused as to how that happens (to debug)
• the failure message will be completely unrelated to the actual error

For some reason i'm not sure to understand yet, in 2.1 and 2.2 the error appears but only during opam install which means it is ignored. In 2.2 the error appears in opam pin and makes the command fail. I think this is something that we want to keep but it also means this is an unknowingly breaking change, although not critical as the fix is fairly straightforward and the case where people use git-lfs is fairly rare. Nevertheless i've added it to the 2.3.1 milestone while we figure things out.

Testing the issue locally can be done using:

$ GIT_LFS_SKIP_SMUDGE=1 git clone https://github.com/hackwaly/ocamlearlybird
$ opam pin -n ./ocamlearlybird