Merge branch 'bugfix/2.7/change-include-for-ci' into 'releases/2.7'

Fetch default yml files via different project instead of url

See merge request core/dune-istl!399

.gitlab-ci.yml

 ---
 include:
-  - "https://gitlab.dune-project.org/core/ci-config/raw/master/config/common/releases/2.7.yml"
-  - "https://gitlab.dune-project.org/core/ci-config/raw/master/jobs/common/releases/2.7.yml"
+  - project: 'core/ci-config'
+    ref: master
+    file: 'config/common/releases/2.7.yml'
+  - project: 'core/ci-config'
+    ref: master
+    file: 'jobs/common/releases/2.7.yml'
 
 before_script:
   - duneci-install-module https://gitlab.dune-project.org/core/dune-common.git