docs(s3): update ID of the example encrypted bucket in the ReadMe (#13436)

The id in the example was misnamed and can cause confusion.


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Author: maoshouse

packages/@aws-cdk/aws-s3/README.md

@@ -43,7 +43,7 @@ new Bucket(this, 'MyFirstBucket');
 Define a KMS-encrypted bucket:
 
 ```ts
-const bucket = new Bucket(this, 'MyUnencryptedBucket', {
+const bucket = new Bucket(this, 'MyEncryptedBucket', {
     encryption: BucketEncryption.KMS
 });