chore(deps): bump actions/download-artifact from 4.3.0 to 6.0.0 (ietf-tools#9805)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4.3.0 to 6.0.0.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4.3.0...v6.0.0)

---
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>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -186,7 +186,7 @@ jobs:
 
     - name: Download a Coverage Results
       if: ${{ github.event.inputs.skiptests == 'false' || github.ref_name == 'release' }}
-      uses: actions/download-artifact@v4.3.0
+      uses: actions/download-artifact@v6.0.0
       with:
         name: coverage
 
@@ -291,7 +291,7 @@ jobs:
 
     - name: Download Coverage Results
       if: ${{ github.event.inputs.skiptests == 'false' || github.ref_name == 'release' }}
-      uses: actions/download-artifact@v4.3.0
+      uses: actions/download-artifact@v6.0.0
       with:
         name: coverage