Add GitLab CI for verification.
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
new file mode 100644
index 0000000..aa2dc0b
--- /dev/null
+++ b/.gitlab-ci.yml
@@ -0,0 +1,9 @@
+stages:
+  - verify
+
+image: maven:3-openjdk-17
+
+verify-job:
+  stage: verify
+  script:
+    - mvn verify