Nearly every time the OxCaml opam repository is updated, our GitHub Actions
break and likewise following the installation instructions from the Wiki fails.
Hopefully we can avoid this churn by pinning that repository to a particular
commit.
The `ocamlformat` changes in this commit are the consequence of a version update;
I've suppressed comment formatting to avoid most of the churn.
Signed-off-by: Kevin Svetlitski <ksvetlitski@janestreet.com>
Kevin Svetlitski
76f4f54ffd