project.py: Remove extraneous ','

Bug: https://crbug.com/1061473
Change-Id: I0f02f122d6313679c1ae5ad6fb4e05f68b764186
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/263112
Tested-by: George Engelbrecht <engeg@google.com>
Reviewed-by: George Engelbrecht <engeg@google.com>
Reviewed-by: SPA SARC <spanc.sarc@gmail.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

project.py

@@ -2678,7 +2678,7 @@ class Project(object):
         if verbose:
           print('%s: Unable to retrieve clone.bundle; ignoring.' % self.name)
           if output:
-            print('Curl output:\n%s', % output)
+            print('Curl output:\n%s' % output)
         return False
       elif curlret and not verbose and output:
         print('%s' % output, file=sys.stderr)