lib/pull: Skip ostree_repo_resolve_keyring_for_collection for bindings

lib/pull: Skip ostree_repo_resolve_keyring_for_collection for bindings

Since ostree_remote_get_type is not made available to g-ir-scanner, it
treats OstreeRemote as a bare struct. That's not kosher for bindings and
it issues the following warning:

  src/libostree/ostree-repo-pull.c:5560: Warning: OSTree:
  ostree_repo_resolve_keyring_for_collection: return value: Invalid
  non-constant return of bare structure or union; register as boxed type
  or (skip)

For now, just skip this API for bindings.

Closes: #1322
Approved by: pwithnall