Bump actions/download-artifact from 3 to 4 (G-Research#288)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 3 to 4.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v3...v4)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  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>
Co-authored-by: Marcin Krystianc <marcin.krystianc@gmail.com>

.github/workflows/ci.yml

@@ -187,7 +187,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download NuGet package artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: nuget-packages
           path: dist
@@ -203,7 +203,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download NuGet package artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: nuget-packages
           path: dist