Enable Linux CI

.gitlab-ci.yml

+# SPDX-FileCopyrightText: None
+# SPDX-License-Identifier: CC0-1.0
+
+include:
+  #- https://invent.kde.org/sysadmin/ci-tooling/raw/master/invent/ci-reuse.yml
+  - 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'
+    'frameworks/kcmutils': '@stable'
+    'frameworks/ki18n': '@stable'
+    'frameworks/kcoreaddons': '@stable'
+    'frameworks/kdbusaddons': '@stable'
+    'frameworks/kdeclarative': '@stable'
+    'frameworks/kwallet': '@stable'
+    'frameworks/kio': '@stable'