Update actions/upload-pages-artifact action to v2

Author: renovate[bot]

.github/workflows/apiref.yml

@@ -42,7 +42,7 @@ jobs:
         run: "cp apigen/favicon.png docs/favicon.png"
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v1
+        uses: actions/upload-pages-artifact@v2
         with:
           path: 'docs'