past upgrades can fail if the caddy config is too long

[ByToddwords]

  File "/usr/local/bin/disco_update", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/disco/app/disco/scripts/update.py", line 71, in main
    task(image)
  File "/disco/app/disco/scripts/update.py", line 208, in task_0_28_x
    _run_cmd(
  File "/disco/app/disco/scripts/update.py", line 93, in _run_cmd
    process = subprocess.Popen(
              ^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/subprocess.py", line 1028, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/local/lib/python3.12/subprocess.py", line 1963, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
OSError: [Errno 7] Argument list too long: 'docker'

this is for a disco with hundreds of projects