Add the new Salsa CI pipeline to this repository

debian/.gitlab-ci.yml

+# For more information please see https://salsa.debian.org/salsa-ci-team/pipeline
+
+include: https://salsa.debian.org/salsa-ci-team/pipeline/raw/master/salsa-ci.yml
+
+build:
+    extends: .build-unstable
+
+reprotest:
+    extends: .test-reprotest
+
+lintian:
+    extends: .test-lintian
+
+autopkgtest:
+    extends: .test-autopkgtest
+
+piuparts:
+    extends: .test-piuparts
+