build(deps): bump actions/download-artifact from 5 to 6 (#5440)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/coverage.yml

@@ -68,7 +68,7 @@ jobs:
           rm -rf coverage
           mkdir coverage
       - name: Download coverage report artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: snapcraftio-coverage
           path: coverage
@@ -112,7 +112,7 @@ jobs:
       - uses: actions/checkout@v5
 
       - name: Download coverage report artifact
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: snapcraftio-coverage
           path: coverage