fix: Potential fix for code scanning alert no. 7: Workflow does not contain permissions

[teolemon]

Potential fix for https://github.com/openfoodfacts/facets-knowledge-panels/security/code-scanning/7

To fix this problem, you should add a permissions key to the workflow YAML file. For maximum clarity and security, add it at the top level, just below the workflow name and event triggers. Review the steps: The workflow uses Crowdin to download/upload translations, and then creates pull requests. According to Crowdin Action documentation and general GitHub Actions usage, it needs ability to read code and create pull requests but does not need full write access to code or issues. Therefore, set contents: read (so workflow jobs can read source and translation files) and pull-requests: write (to allow PR creation).

Edit .github/workflows/crowdin.yml, adding:

permissions:
  contents: read
  pull-requests: write

just after the workflow name and before on: or after on:.

No other code imports or steps need to be changed.

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