Bump actions/upload-pages-artifact from 1 to 2

Bumps [actions/upload-pages-artifact](https://github.com/actions/upload-pages-artifact) from 1 to 2.
- [Release notes](https://github.com/actions/upload-pages-artifact/releases)
- [Commits](actions/upload-pages-artifact@v1...v2)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/ci.yml

@@ -246,7 +246,7 @@ jobs:
             # Upload the template, now containing the built docs, as an artifact that
             # can be accessed by the `deploy-docs` job.
             -   name: Upload GitHub Pages artifact
-                uses: actions/upload-pages-artifact@v1
+                uses: actions/upload-pages-artifact@v2
                 with:
                     path: template