Add ruff format --check

Description

As we have a job for black, a job for ruff and that ruff format "is designed as a drop-in replacement for Black, but with an excessive focus on performance and direct integration with Ruff" I would like to use it instead of black with the --check option, see ruff format doc for more details.

Implementation ideas

spec:
  inputs:
    ruff-format-enabled:
      description: Enable ruff format
      type: boolean
      default: false
...
variables:
  PYTHON_RUFF_FORMAT_ENABLED: $[[ inputs.ruff-format-enabled ]]
...

py-ruff-format:
  extends: .python-base
  stage: build
  script:
    - install_requirements
    - _pip install ruff
    - _run ruff format . --check
  rules:
    # exclude if $PYTHON_RUFF_FORMAT_ENABLED not set
    - if: '$PYTHON_RUFF_FORMAT_ENABLED != "true"'
      when: never
    - !reference [.test-policy, rules]