Update upload-artifact to v4

Author: jdesrosiers

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
       - run: pip install --requirement requirements.txt
       - run: xml2rfc --version
       - run: make all
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@v4
         with:
           name: specification-docs
           path: |