sync: fix print error when handling server error

When converting this logic from print() to the output buffer, this
error codepath should have dropped the use of the file= redirect.

Bug: https://crbug.com/gerrit/14482
Change-Id: Ib484924a2031ba3295c1c1a5b9a2d816b9912279
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/305142
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

project.py

@@ -1051,7 +1051,7 @@ class Project(object):
                        prune=False,
                        submodules=False,
                        clone_filter=None,
-                       partial_clone_exclude=None):
+                       partial_clone_exclude=set()):
     """Perform only the network IO portion of the sync process.
        Local working directory/branch state is not affected.
     """
@@ -2205,7 +2205,7 @@ class Project(object):
 
       # Figure out how long to sleep before the next attempt, if there is one.
       if not verbose:
-        output_redir.write('\n%s:\n%s' % (self.name, gitcmd.stdout), file=sys.stderr)
+        output_redir.write('\n%s:\n%s' % (self.name, gitcmd.stdout))
       if try_n < retry_fetches - 1:
         output_redir.write('sleeping %s seconds before retrying' % retry_cur_sleep)
         time.sleep(retry_cur_sleep)