[BUGFIX] Could not fetch from bitbucket

When installing Sphinx, a snapshot of repository sphinx-contrib
cannot be fetched.

Change-Id: I9bb10605c396415ce2730947f516fe78b74e5706
Fixes: #59290
Reviewed-on: https://review.typo3.org/30524
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers