explicit build env for pixi build

[sanathkeshav]

Checklist:

• I made sure that the CI passed before I ask for a review.
• I added a summary of the changes (compared to the last release) in the CHANGELOG.md.
• If necessary, I made changes to the documentation and/or added new content.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[sanathkeshav]

@claudiushaag, although the tests pass, in the normal Build and Test workflow (jammy & noble), runs the tests with Ctest and runs pixi run -e dashboard pytest.

Surprisingly, this triggers the Pixi build (should not happen) only in Noble but not in Jammy. Am I doing something wrong?