Bump actions/download-artifact from 4 to 8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...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.yml

@@ -320,7 +320,7 @@ jobs:
 
       # Download artifacts from previous 'tests' job
       - name: Download coverage artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
 
       # Now attempt upload to Codecov using its action.
       # NOTE: We use a retry action to retry the Codecov upload if it fails the first time.

.github/workflows/docker.yml

@@ -80,7 +80,7 @@ jobs:
         uses: actions/checkout@v4
       # Download Docker image artifacts (which were just built by reusable-docker-build.yml)
       - name: Download Docker image artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           # Download all amd64 Docker images (TAR files) into the /tmp/docker directory
           pattern: docker-image-*-linux-amd64