Bump actions/download-artifact from 5.0.0 to 6.0.0 (#4365)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5.0.0 to 6.0.0.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](634f93cb29...018cc2cf5b)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/build.yaml

@@ -260,7 +260,7 @@ jobs:
 
       - name: Get self-signed certificate from the prepare job
         if: ${{ needs.prepare.outputs.self_signed_cert == 'true' }}
-        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
         with:
           name: signing-key
 

.github/workflows/test.yaml

@@ -57,7 +57,7 @@ jobs:
 
       - name: Get OS image artifact
         if: ${{ inputs.use-artifact }}
-        uses: actions/download-artifact@634f93cb2916e3fdff6788551b99b062d0335ce0 # v5.0.0
+        uses: actions/download-artifact@018cc2cf5baa6db3ef3c5f8a56943fffe632ef53 # v6.0.0
         with:
           name: haos_ova-${{ inputs.version }}.qcow2.xz