Bump actions/upload-pages-artifact from 3 to 4 (#149)

Author: dependabot[bot]

.github/workflows/docs.yaml

@@ -32,7 +32,7 @@ jobs:
       - name: Build Doxygen Site
         run: cmake --build build --target docs
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@v4
         with:
           path: build/docs/html
       - name: Deploy to GitHub Pages