Use wheel.exclude rather than sdist.exclude for wrapper sources (#4428)

sdist.exclude = ["*.cpp"] removed the twelve nanobind wrapper sources
from the sdist, not just from the wheel. Since nanobind_add_module()
refers to them by name, an sdist built this way cannot be compiled.

No sdist has ever been shipped, so nothing already published is
affected; this is a latent problem rather than a live one.

wheel.exclude keeps the sources out of the wheel, which is what was
intended, while leaving the sdist buildable.

Verified by building both artefacts: the sdist now carries all twelve
dolfinx/wrappers/*.cpp files and the wheel carries none, with the
sixteen dolfinx_wrappers/*.h headers present in both as before.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: jhale

python/pyproject.toml

@@ -87,7 +87,7 @@ ci = [
 
 [tool.scikit-build]
 wheel.packages = ["dolfinx"]
-sdist.exclude = ["*.cpp"]
+wheel.exclude = ["*.cpp"]
 cmake.build-type = "Release"
 
 [tool.scikit-build.cmake.define]