Update .gitlab-ci.yml file

.gitlab-ci.yml

-image: python:3.9.2-buster
-
-stages:
-  - deploy_stage
-  - deploy_prod
-
-before_script:
-   - pip install twine
-   - python setup.py sdist
+deploy_staging:
+  stage: deploy
+  variables:
+    TWINE_USERNAME: $STAGING_USERNAME
+    TWINE_PASSWORD: $STAGING_PASSWORD
+  script:
+    - twine upload --repository testpypi dist/* --verbose
+  except:
+    - tags
 
 deploy_production:
-  stage: deploy_prod
+  stage: deploy
   variables:
     TWINE_USERNAME: __token__
     TWINE_PASSWORD: $PRODUCTION_PASSWORD
   script:
     - twine upload --repository-url https://upload.pypi.org/legacy/ dist/* --verbose
+  only:
+    - tags
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