Bump actions/download-artifact from 3 to 4 xarray-contrib/datatree#295

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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/pypipublish.yaml

@@ -52,7 +52,7 @@ jobs:
         name: Install Python
         with:
           python-version: '3.10'
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v4
         with:
           name: releases
           path: dist
@@ -72,7 +72,7 @@ jobs:
     if: github.event_name == 'release'
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/download-artifact@v3
+      - uses: actions/download-artifact@v4
         with:
           name: releases
           path: dist