ci: fixes codesandbox CI by setting node version in ci.json (#1616)

Note: the same thing was done in the past to fix the same problem for `drei` pmndrs/drei#417

Author: smhutch

.codesandbox/ci.json

@@ -1,3 +1,4 @@
 {
-  "sandboxes": ["/example"]
+  "sandboxes": ["/example"],
+  "node": "14"
 }