Merge pull request #12428 from nextcloud/fix/ncu/filter-since-tag

filter @SInCE in NCU/

developer_manual/digging_deeper/api.rst

@@ -18,6 +18,7 @@ first version of the future API in the `NCU` namespace, following these rules:
 - Files are located in ``/lib/unstable/``
 - Code quality, comments, tests and psalm check are expected to be identical to the `OCP` namespace.
 - Classes must be tag as ``@experimental``, including the current version of Nextcloud.
+- Tag ``@since`` must not be used in the `NCU` namespace.
 - Code from the `OCP` namespace must never mention anything coming from the `NCU` namespace. It can not require it as an argument, constant or return something from `NCU`.
 - An API can only live in this unstable namespace for one major release.
 - During this testing phase, the code and the API can be modified/restructured without limitation.