Why does gitlab-runner run ruby's docker executor even though shell is specified?

Question

GitLab

Here is the gitlab-ci file

stages:
  - deploy
deploy:
  stage: deploy
  script:
    - npm install
    - npm run build
    - cp -R build/* /var/www/html

when pushing, it launches a pipeline in which
Preparing the "docker+machine" executor
00:28
Using Docker executor with image ruby:2.5 ...

because of this, the runner does not see npm
npm install
/bin/bash: line 110: npm: command not found

Here is the config file from the server config.toml
concurrent = 1
check_interval = 0

[session_server]
session_timeout = 1800


name = "test"
url = " https://gitlab.com/ "
token = "123321123"
executor = "shell"
shell = "bash"
[runners.custom_build_dir]
[runners.cache]
[runners.cache.s3]
[runners.cache.gcs]
[runners.cache.azure]