Upgrade GitHub Actions to latest versions

[salmanmkc]

Summary

This PR upgrades GitHub Actions to their latest versions for Node.js 24 compatibility and security updates.

Changes

Action	Old Version(s)	New Version	Files
Jimver/cuda-toolkit	v0.2.29	v0.2.30	build_kernel_windows.yaml
actions/attest-build-provenance	v2	v3	kernel_abi_python_release.yaml
astral-sh/setup-uv	v5	v7	lint.yml, test_kernels.yaml, test_python.yaml
cachix/cachix-action	v14, v15	v16	build_kernel_macos.yaml, build_kernel_rocm.yaml, test_extra_commands.yaml
cachix/install-nix-action	v27	v31	check_variants.yaml, nix_fmt.yaml
sigstore/gh-action-sigstore-python	v3.0.0	v3.2.0	publish_kernels.yml

Why these changes?

• Keeps actions up to date with latest stable releases
• Updated actions include security fixes and new features

Testing

These changes only update action versions and don't modify workflow logic.