ci: bump upload-pages-artifact to v4.0.0 to satisfy SHA-pinning policy (#301)

actions/upload-pages-artifact@v3 transitively calls
actions/upload-artifact@v4 as a floating tag, which the repo's
full-SHA pinning policy rejects, failing the docs deploy at job
setup. v4.0.0 pins its internal upload-artifact to a SHA (v4.6.2).

Fixes #300

Signed-off-by: Kyle Hounslow <kylhouns@amazon.com>

Author: kylehounslow

.github/workflows/docs-deploy.yml

@@ -61,7 +61,7 @@ jobs:
           cp -r starlight-docs/dist/* dist/docs/
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@56afc609e74202658d3ffba0e8f6dda462b719fa # v3
+        uses: actions/upload-pages-artifact@7b1f4a764d45c48632c6b24a0339c27f5614fb0b # v4.0.0
         with:
           path: ./docs/dist