Fix usage of bare 'except'

flake8 reports:

  E722 do not use bare 'except'

Replace them with 'except Exception' per [1] which says:

  Bare except will catch exceptions you almost certainly don't want
  to catch, including KeyboardInterrupt (the user hitting Ctrl+C) and
  Python-raised errors like SystemExit

  If you don't have a specific exception you're expecting, at least
  except Exception, which is the base type for all "Regular" exceptions.

[1] https://stackoverflow.com/a/54948581

Change-Id: Ic555ea9482645899f5b04040ddb6b24eadbf9062
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254606
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: David Pursehouse <dpursehouse@collab.net>

subcmds/sync.py

@@ -603,7 +603,7 @@ later is required to fix a server side protocol bug.
           bare_git.gc('--auto', config=config)
         except GitError:
           err_event.set()
-        except:
+        except Exception:
           err_event.set()
           raise
       finally: