build(deps): bump actions/download-artifact from 7 to 8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 7 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v7...v8)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '8'
  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

@@ -203,7 +203,7 @@ jobs:
           save-always: true # always save the cache, even if build fails
 
       - name: Download Linuxkit artifacts
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         if: ${{ github.ref != 'refs/heads/main' }}
         with:
           name: linuxkit-images-${{ matrix.docker_arch }}
@@ -223,7 +223,7 @@ jobs:
           docker images
 
       - name: Download Kernel artifacts
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         if: ${{ github.ref != 'refs/heads/main' }}
         with:
           name: kernel-images-${{ matrix.kernel }}
@@ -273,7 +273,7 @@ jobs:
         uses: actions/checkout@v6
 
       - name: Download built Hook artifacts
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         with:
           pattern: "hook-tarball-*"
           merge-multiple: true
@@ -345,7 +345,7 @@ jobs:
         uses: actions/checkout@v6
 
       - name: Download built Hook artifacts
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         with:
           pattern: "hook-tarball-*"
           merge-multiple: true