Fix YAML anchors

[JenswBE]

Description

Fixes #559.
Based on https://eemeli.org/yaml/#schema-options.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I've read & comply with the contributing guidelines
• I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• I have made corresponding changes to the documentation (README.md).
• I've checked my modifications for any breaking changes, especially in the config.yml file

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[bastienwirtz]

Hi @JenswBE,
Thanks for your contribution !
Looks good to me 👍