Fix broken links

External Link checker complains about two broken links.

• Error at https://gfz-potsdam.de
• Error at https://gitlab.hzdr.de/help/ci/README.md @erxleb87 @frust45 @hueser93 Don't know where this is now. Can one of you please check?

_posts/2021/02/2021-02-09-helmholtz-gitlab.md

@@ -72,7 +72,7 @@ with the published [Ansible roles][roles].
 [issue-tracker]: https://gitlab.hzdr.de/help/user/project/issues/index.md#issues-list
 [merge-requests]: https://gitlab.hzdr.de/help/user/project/merge_requests/index.md
 [issue-boards]: https://gitlab.hzdr.de/help/user/project/issues/index.md#issue-boards
-[ci]: https://gitlab.hzdr.de/help/ci/README.md
+[ci]: https://gitlab.hzdr.de/help/ci/index.md
 [registry]: https://gitlab.hzdr.de/help/user/packages/container_registry/index.md
 [pages]: https://gitlab.hzdr.de/help/user/project/pages/index.md
 [packages]: https://gitlab.hzdr.de/help/user/packages/package_registry/index.md