Add reuse lint via gitlab ci

.gitlab-ci.yml

+# SPDX-FileCopyrightText: 2024 Philip Bergmann <philip.bergmann@uni-wuerzburg.de>
+# SPDX-License-Identifier: CC0-1.0
+
+default:
+  # run on the linux docker runners
+  tags:
+  - linux
+  - docker
+
+# Snippet from https://reuse.software/dev/
+reuse:
+  image:
+    name: fsfe/reuse:latest
+    entrypoint: [""]
+  script:
+    - reuse lint