Bump actions/download-artifact from 2 to 3

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 2 to 3.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v2...v3)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/main.yaml

@@ -34,7 +34,7 @@ jobs:
     if: github.event_name == 'push'
     steps:
       - name: Download builds
-        uses: actions/download-artifact@v2
+        uses: actions/download-artifact@v3
         with:
           name: px4_msgs
           path: bin