bump actions/upload-artifact from v2 to v4 (#2286)

Our Docker build action currently uses `actions/upload-artifact@v2` to
upload the PhysioNet image to DockerHub. v2 was deprecated on 30 June
2024: https://github.com/actions/upload-artifact

> actions/upload-artifact@v3 is scheduled for deprecation on November
30, 2024. [Learn
more.](https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/)
Similarly, v1/v2 are scheduled for deprecation on June 30, 2024. Please
update your workflow to use v4 of the artifact actions. This deprecation
will not impact any existing versions of GitHub Enterprise Server being
used by customers.

.github/workflows/docker-build-test.yml

@@ -53,7 +53,7 @@ jobs:
 
       - name: Upload physionet image
         if: github.ref == 'refs/heads/dev' || github.event.inputs.publish_tag
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: physionet
           path: /tmp/physionet.tar.gz