Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](https://github.com/actions/download-artifact/compare/v5...v6)

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

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

.github/workflows/openwrt-2410-snapshot-build.yml

@@ -221,7 +221,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Download artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: OpenWrt Docker Image
           path: .

.github/workflows/openwrt-master-build.yml

@@ -223,7 +223,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Download artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: OpenWrt Docker Image
           path: .

.github/workflows/openwrt-stable-build.yml

@@ -215,7 +215,7 @@ jobs:
         uses: actions/checkout@v5
 
       - name: Download artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: OpenWrt Docker Image
           path: .