pixi build - variants + recipe.yaml gives an error: Error: expected the build backend to return a single built package but it returned 2

[wolfv]

Checks

• [x] I have checked that this issue has not already been reported.

• [x] I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

[workspace]
authors = ["Wolf Vollprecht <[email protected]>"]
channels = ["conda-forge"]
description = "Add a short description here"
name = "build-recipe"
platforms = ["osx-arm64"]
version = "0.1.0"
preview = ["pixi-build"]

[workspace.build-variants]
python = ["3.10.*", "3.11.*"]

[dependencies]
with-variants = { path = "./recipe" }
python = "3.10.*"

And

package:
  name: with-variants
  version: 0.1.0

requirements:
  host:
    - python

Issue description

Error: × expected the build backend to return a single built package but it returned 2

This should not be the case - we should only build the python 3.10 package in this case and not error like this.

Expected behavior

Build only a single package and not complain / error.