Bump actions/upload-artifact from 3 to 4

Author: tkoyama010

.github/workflows/test.yml

@@ -36,7 +36,7 @@ jobs:
       #   run: |
       #     make doctest
       - name: Stash coverage
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: coverage.xml
           path: coverage.xml