Enable Linux CI

.gitlab-ci.yml

+# SPDX-FileCopyrightText: None
+# SPDX-License-Identifier: CC0-1.0
+
+include:
+  - https://invent.kde.org/sysadmin/ci-utilities/raw/master/gitlab-templates/linux.yml

.kde-ci.yml

+# SPDX-FileCopyrightText: None
+# SPDX-License-Identifier: CC0-1.0
+
+Dependencies:
+- 'on': ['@all']
+  'require':
+    'frameworks/extra-cmake-modules': '@stable'