Fix code snippet (#12446)

Author: Luca Forstner

docs/platforms/javascript/common/session-replay/understanding-sessions.mdx

@@ -192,7 +192,7 @@ If you want to skip capturing a Replay for certain errors, you can use the `befo
 replayIntegration({
   beforeErrorSampling: (event) => {
     // Return false to skip capturing a Replay for this error
-    return !event.exception?.values?.[0]?.message?.includes("drop me");
+    return !event.exception?.values?.[0]?.value?.includes("drop me");
   },
 });
 ```