How can I restrict deploy stage only be used in upstream repository not in forked repository

I problem I found was when I forked upstream repository to my repository. While I was developing and pushing to my repository, the gitlab-ci ran tasks that had written in gitlab-ci.yml. The test task had been executed and deploy task also but I did not want the deploy task to be executed in forked branch.

This is my current gitlab-ci.yml

stages:
  - build
  - test
  - deploy

cache:
  key: "$CI_BUILD_REF_NAME"
  untracked: true
  paths:
  - node_modules/

perform-testing:
 stage: test
 script:
   - npm test
 tags:
   - docker

development-push:
  stage: deploy
  environment: development
  script:
   - DO_SOME_TASK
  tags:
    - shell
  only:
    - development

staging-push:
  stage: deploy
  environment: staging
  script:
    - DO_SOME_TASK
  tags:
    - shell
  only:
    - master

Was this problem already solved before ? Any solutions on the current gitlab-ci ?