doc: omit publishing internal odoc files: .odocl

Context

The online doc on tezos.gitlab.io contains a large amount of internal files produced by Odoc, bearing extension .odocl. (See http://ocaml.github.io/odoc/interface.html) These files, totaling almost 0.5G, should not be published by the CI job documentation:publish to save space.

This MR proposes a minimal change for that.

Manually testing the MR

Build the doc locally or in the CI, and check that directory docs/_build/api/odoc contains only three directories:

_html/	_mlds/	_odoc/

Then take a look to the doc artifacts of another doc MR, such as !11180 (merged), and see that it contains 4 directories

_html/	_mlds/	_odoc/    _odocls/

Checklist

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