Proto/Michelson: add a forgotten tailcall annotation

Context

All recursive calls but one in Script_typed_ir.ty_traverse are annotated with [@ocaml.tailcall]. This MR adds the annotation for the forgotten case.

This was found by attempting to generate this function using Polyrun and looking at the diff.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR