Deployment incorrectly triggered (conditional not honored)

Deployment
4

Interestingly, I have a deploy block, just like described in the official documentation, which only ran for pushed tags in the past, but now it seems to be running for all changes on the main branch.

Code snippet and example of failing build:

  - stage: deploy
    python: 3.7
    env:
    install: skip
    script: skip
    deploy:
      provider: pypi
      distributions: sdist bdist_wheel
      user: ...
      password:
        secure: ...
      on:
        tags: true

P.S.: user: should also be exchanged by username:in the documentation according to the linter