Ninja and Cmake should not be in pyproject's build-system.requires

[adraub]

While trying to rebuild the mlc-z3-static package, i ran into this warning:

| * Getting build dependencies for wheel...
| * Building wheel...
| 2026-08-30 18:07:31,030 - scikit_build_core - WARNING - cmake should not be in build-system.requires - scikit-build-core will inject it as needed
| 2026-08-30 18:07:31,030 - scikit_build_core - WARNING - ninja should not be in build-system.requires - scikit-build-core will inject it as needed
| *** scikit-build-core 0.12.2 using CMake 4.3.1 (wheel)

The correct way seems to be using:

...
[build-system]
requires = ["scikit-build-core"]
build-backend = "scikit_build_core.build"
...

[tool.scikit-build.cmake]
minimum-version = "3.26"
...