This job is stuck, because the project doesn't have any runners online assigned to it. Go to Runners page

The job is stuck because your runners have tags but your jobs don't. Follow these 4 steps to enable your runner to run without tags:

enter image description here

Or set tags to your jobs. For more info: Configuration of your jobs with .gitlab-ci.yml - Tags

Make sure you are using the correct tag i.e. whatever present corresponding to the configured runner for your project.

In your case it would be like :

maven-build:
 image: maven:3-jdk-8
 stage: build
 tags: my project ci-cd
 script: "mvn package -B"
 artifacts:
 paths:
  - target/*.jar

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