Bump dawidd6/action-download-artifact from 16 to 18 (#276)

Bumps [dawidd6/action-download-artifact](https://github.com/dawidd6/action-download-artifact) from 16 to 18.
- [Release notes](https://github.com/dawidd6/action-download-artifact/releases)
- [Commits](dawidd6/action-download-artifact@v16...v18)

---
updated-dependencies:
- dependency-name: dawidd6/action-download-artifact
  dependency-version: '18'
  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/build-lcg-cvmfs.yml

@@ -280,7 +280,7 @@ jobs:
 
       - name: Download target branch artifacts (prompt summary)
         if: github.event_name == 'pull_request'
-        uses: dawidd6/action-download-artifact@v16
+        uses: dawidd6/action-download-artifact@v18
         with:
           workflow: build-lcg-cvmfs.yml
           branch: ${{ github.event.pull_request.base.ref }}
@@ -290,7 +290,7 @@ jobs:
 
       - name: Download target branch artifacts (regalias)
         if: github.event_name == 'pull_request'
-        uses: dawidd6/action-download-artifact@v16
+        uses: dawidd6/action-download-artifact@v18
         with:
           workflow: build-lcg-cvmfs.yml
           branch: ${{ github.event.pull_request.base.ref }}