fix: regression in CopyObject not preserving ETag in --compat (#9322)

issue found after `git bisect` to commit db41953618

cmd/object-handlers.go

@@ -993,9 +993,11 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 				return
 			}
 
+			if isTargetEncrypted {
 				pReader = NewPutObjReader(rawReader, srcInfo.Reader, &objEncKey)
 			}
 		}
+	}
 
 	srcInfo.PutObjReader = pReader