fix the CI builds a bit

[shayne-fletcher]

the .github workflows have been failing for some time. it would seem in fd0c69d the directory shim/third-party/ocaml/ got removed which has resulted in the ./ocaml-setup.sh step in the workflows failing. this PR restores shim/third-party/ocaml/opam and the builds get further (the cargo build and test workflow succeeds in my testing)

[facebook-github-bot]

Hi @shayne-fletcher!

Thank you for your pull request.

We require contributors to sign our Contributor License Agreement, and yours needs attention.

You currently have a record in our system, but the CLA is no longer valid, and will need to be resubmitted.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at [email protected]. Thanks!

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Meta Open Source project. Thanks!