Update notes for submitted changes

* Wait opening new packfile until it can't be racy anymore

8b/f9c668adca33166057e7137d52a509d232acb3

+Verified+1: CI Bot
+Code-Review+2: Matthias Sohn <matthias.sohn@sap.com>
+Submitted-by: Christian Halstrick <christian.halstrick@sap.com>
+Submitted-at: Wed, 05 Jun 2019 09:22:23 -0400
+Reviewed-on: https://git.eclipse.org/r/141843
+Project: jgit/jgit
+Branch: refs/heads/stable-5.1