gitlab.rst: Fix redundant 'project' word

'main_project_name' is defined as 'Oniro Porject' so this cleans up the
sentence that would end up: "Oniro Project project".

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

contributing/gitlab.rst

@@ -13,7 +13,7 @@ Gitlab Contributions
 Overview
 ********
 
-|main_project_name| project handles contributions as `merge requests <https://docs.gitlab.com/ee/user/project/merge_requests/>`_
+|main_project_name| handles contributions as `merge requests <https://docs.gitlab.com/ee/user/project/merge_requests/>`_
 to relevant repositories part of the |main_project_name| `GitLab instance <https://gitlab.eclipse.org/eclipse/oniro-core>`_.
 The flow for handling that is classic: fork-based merge requests. This means
 that once you have an account, you can fork any repository, create a branch