Bump actions/upload-artifact from 2 to 3

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

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

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

.github/workflows/build.yml

@@ -40,7 +40,7 @@ jobs:
           mkdocs --version
 
       - name: Package website
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: generated-site
           path: site.tar

.github/workflows/deploy.yml

@@ -47,7 +47,7 @@ jobs:
           mkdocs --version
 
       - name: Package website
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v3
         with:
           name: generated-site
           path: site.tar