ci: Fix ci reference from the manifest repository

The ci used to be a document in the manifest repository (aggregated in
docs as a symlink). On the manifest repository side, the topic was
restructured switching ci to a directory. Fix the reference in the docs
aggregation.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

ci/manifest.rst

@@ -6,4 +6,4 @@ The manifest Repository
 =======================
 
 Refer to the section about :doc:`CI in manifest repository
-</repos/manifest/ci>`.
+</repos/manifest/ci/index>`.