Upload dist artifacts to GitHub Actions (#1003)

This adds an [upload artifact](https://github.com/actions/upload-artifact)
Github action step to store the results of the build in the Github Actions
workflow.

This allows us to download the artifacts from the Github Actions UI.
Sometimes it's useful to have the artifacts available for debugging
purposes, or to test a branch in an application before merging.

.github/workflows/ci.yml

@@ -35,3 +35,8 @@ jobs:
 
     - name: Firefox Test
       run: yarn test:browser --project=firefox
+
+    - uses: actions/upload-artifact@v3
+      with:
+        name: turbo-dist
+        path: dist/*