Bump actions/download-artifact from 2 to 4 in /.github/workflows (#17)

* Bump actions/download-artifact from 2 to 4 in /.github/workflows

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 2 to 4.1.7.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v2...v4.1.7)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

* Update main.yml

---------

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

.github/workflows/main.yml

@@ -55,7 +55,7 @@ jobs:
 
       # download the doc files, most of which are generated above
       - name: Download output directory
-        uses: actions/download-artifact@v2
+        uses: actions/download-artifact@v4
         with:
           name: doc-files
           path: docs
@@ -70,4 +70,4 @@ jobs:
             "docs/mobilitydb-berlinmod.pdf", 
             "docs/mobilitydb-berlinmod.epub",
             "docs/html/docbook.css", "docs/html/images/*",
-            "docs/html/*.html"]'
+            "docs/html/*.html"]'