build(deps): bump actions/upload-artifact from 4 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/build-all-matrix.yaml

@@ -101,7 +101,7 @@ jobs:
         run: bash build.sh linuxkit-containers
 
       - name: Upload Linuxkit Docker images as GitHub Artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: linuxkit-images-${{ matrix.docker_arch }}
           path: ${{ runner.temp }}/*-${{ matrix.docker_arch }}.tar.gz
@@ -146,7 +146,7 @@ jobs:
         run: bash build.sh build-kernel "${{ matrix.kernel }}"
 
       - name: Upload Kernel Docker images as GitHub Artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: kernel-images-${{ matrix.kernel }}
           path: ${{ runner.temp }}/hook-kernel-*.tar.gz
@@ -259,7 +259,7 @@ jobs:
         run: bash build.sh build "${{ matrix.kernel }}" LINUXKIT_ISO=yes
 
       - name: Upload deb as artifact ${{ matrix.arch.name }} ${{ matrix.distro }}
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: "hook-tarball-${{ matrix.kernel }}"
           path: |