cmd/ethkey: fix file permissions in changepassword command (#20313)

Found by staticcheck.

cmd/ethkey/changepassword.go

@@ -77,7 +77,7 @@ Change the password of a keyfile.`,
 		}
 
 		// Then write the new keyfile in place of the old one.
-		if err := ioutil.WriteFile(keyfilepath, newJson, 600); err != nil {
+		if err := ioutil.WriteFile(keyfilepath, newJson, 0600); err != nil {
 			utils.Fatalf("Error writing new keyfile to disk: %v", err)
 		}