progress: Ignore updates after progress ends

This addresses the occasional "..working.." message at the end of sync.

Bug: 503869525
Change-Id: I489d29fa8ae588d77abb7fee5f157800d4abb368
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/574482
Commit-Queue: Gavin Mak <gavinmak@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Becky Siegel <beckysiegel@google.com>

Author: gavinmak

progress.py

@@ -159,6 +159,8 @@ def update(self, inc=1, msg=None):
             inc: The number of items completed.
             msg: The message to display. If None, use the last message.
         """
+        if self._ended:
+            return
         self._done += inc
         if msg is None:
             msg = self._last_msg