gh-38554: Fix conda environments after `build` was removed from conda-forge in favor of `python-build`
- Fixes https://github.com/sagemath/sage/issues/38550
### :memo: Checklist
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
### :hourglass: Dependencies
None.
URL: https://github.com/sagemath/sage/pull/38554
Reported by: Ricardo Buring
Reviewer(s):
