The difference between running a docker image form a gitlab-runner or directly

Question

I need a customised maven docker image to execute my tests.
It requires me to tweak the time zone and add true type fonts.
I created my own maven image FROM maven:3.6.3-openjdk-8
I am using the gitlab/gitlab-ce:latest locally on my Mac and executing my tests in two ways

1. From the container shell

docker run -it -v /Users/myuser/.m2:/root/.m2 -v \
    /local/config:/local/ config -v \
    /Users/ myuser /workspace/:/build \
    --network=mynetwrok \
    maven- tweak:1.0.1 bash

2. from the local gitlab with the following runner config

oncurrent = 1
check_interval = 0

 [session_server]
   session_timeout = 1800

 [[runners]]
   name = "maven- tweak "
   url = "http://gitlab"
   token = "xyz"
   executor = "docker"
   [runners.custom_build_dir]
   [runners.docker]
     tls_verify = false
     image = "maven- tweak:1.0.0"
     privileged = false
     disable_entrypoint_overwrite = false
     oom_kill_disable = false
     disable_cache = false
     volumes = ["/cache","/Users/myuser/.m2:/root/.m2",“/Users/ myuser/workspace/:/build "]
     network_mode = "mynetwork"
     shm_size = 0
   [runners.cache]
     [runners.cache.s3]
     [runners.cache.gcs]

I am trying to figure it out for a while now.
What are the deferences between the two executions so I could figure out the problems.