Changing `package.build.config` does not invalidate caches

[baszalmstra]

Checks

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

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

Reproducible example

Check out this repository: https://github.com/baszalmstra/pixi-build-backend-config-invalidation-bug

The package contains a noarch python project.

1. Clone https://github.com/baszalmstra/pixi-build-backend-config-invalidation-bug
2. Run pixi lock once in the clone to populate caches. Lockfile should be up-to-date.
3. Comment in the following in the pixi.toml to make to package platform specific

   [package.build.config]
   noarch = false

4. Run pixi lock again. Note that the lock-file is still up-to-date, which is wrong.
5. Delete the cache folder. rm -rf .pixi/build
6. Rerun pixi lock. Note that the lock-file is updated.

Issue description

I think the package.build.config section does not invalidate the backend cache.

Expected behavior

The cache should be updated and the lock-file should have changed as soon as the package is made noarch: false.