Increase timeout for Linux flutter_packaging_test (#162673)

This test increased in time and is timing out. While we search for the
cause, we need to increase the timeout

Author: jtmcdole

.ci.yaml

@@ -684,6 +684,7 @@ targets:
     presubmit: false
     enabled_branches:
       - master
+    timeout: 60 # TODO(https://github.com/flutter/flutter/issues/162654)
     properties:
       task_name: flutter_packaging
       tags: >