Fixed CI to be able to deploy to central maven snapshots.

.gitlab-ci.yml

 image: maven:latest
 
+variables:
+  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode"
+  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"
+
 cache:
   paths:
     - ~/.m2/repository/
+    - .m2/repository/
     - target/
 
 build:
   stage: build
   script:
-    - mvn compile
+    - mvn $MAVEN_CLI_OPTS compile
   tags:
     - general
 
 test:
   stage: test
   script:
-    - mvn test
+    - mvn $MAVEN_CLI_OPTS test
   tags:
     - opencl
 
 deploy:
   stage: deploy
   script:
-    - mvn -DskipTests=true deploy
+    - mvn $MAVEN_CLI_OPTS -DskipTests=true deploy
   tags:
     - general
   only:

.m2/settings.xml

+<settings xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.1.0 http://maven.apache.org/xsd/settings-1.1.0.xsd"
+    xmlns="http://maven.apache.org/SETTINGS/1.1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <servers>
+    <server>
+      <id>ossrh.snapshots</id>
+      <username>${env.MAVEN_REPO_USER}</username>
+      <password>${env.MAVEN_REPO_PASS}</password>
+    </server>
+    <server>
+      <id>ossrh</id>
+      <username>${env.MAVEN_REPO_USER}</username>
+      <password>${env.MAVEN_REPO_PASS}</password>
+    </server>
+  </servers>
+</settings>