Revert the setuptools to <58. Setuptools will silently ignore use_2to3 for 58.0.0
#2086: Removed support for 2to3 during builds. Projects should port to a unified codebase or pin to an older version of Setuptools using PEP 518 build-requires.
But will only fail a build at v58.0.2
#2769: Build now fails fast when use_2to3 is supplied.
Nothing else changed except the requirements and cleaned up pip install vatnumber that is already in the requirements for odoo13. Technically we could also have a fork of vatnumber that doesn't really validate anything and can be used transparently. If you really want to ensure that the tax number are valid, you should really use proper APIs instead of the vatnumber validation.