Create a new object for console to have a prototype with toString met…

…hod (#11834)

* Create a new object to have a prototype

Objects possibly can have null prototypes. This causes them not to have
toString() method leading to an error when doing substitution with
console.warn().

.changeset/rich-geese-complain.md

@@ -0,0 +1,5 @@
+---
+"@apollo/client": patch
+---
+
+Fix error "Cannot convert object to primitive value"

src/cache/inmemory/writeToStore.ts

@@ -873,7 +873,7 @@ For more information about these options, please refer to the documentation:
         " have an ID or a custom merge function, or "
     : "",
     typeDotName,
-    existing,
-    incoming
+    { ...existing },
+    { ...incoming }
   );
 }