我是devops新手，尝试使用Gitlab CI/CD和本地docker runner进行pytest。我的工作失败了，错误如下：

WARNING: Failed to pull image with policy "if-not-present": invalid reference format (manager.go:237:0s)
ERROR: Job failed: failed to pull image "python 3.9" with specified policies [if-not-present]: invalid reference format (manager.go:237:0s)

我该怎么修呢？
我的. gitlab-ci. yml

stages:
  - test

image: python 3.9

run_tests:
  stage: test
  before_script:
    - pip install -r requirements.txt
  script:
    - pytest -v -s
  tags:
    - docker-local

我的本地跑步者. yml

services:
  runner:
    container_name: gitlab-runner
    image: gitlab/gitlab-runner:latest
    volumes:
      - ./runner/:/etc/gitlab-runner
      - /var/run/docker.sock:/var/run/docker.sock
    restart: always

config.toml

concurrent = 1
check_interval = 0
shutdown_timeout = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "test_runner_local"
  url = "https://my_url"
  id = 8
  token = "TOKEN"
  token_obtained_at = data
  token_expires_at = data
  executor = "docker"
  [runners.custom_build_dir]
  [runners.cache]
    MaxUploadedArchiveSize = 0
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    pull_policy = ["if-not-present"]
    tls_verify = false
    image = "python:3.9"
    privileged = false
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    shm_size = 0

如果我删除config.toml中的pull_policy字段或将其值替换为'always'-错误不会消失。