Add update pull_policy for site_worker service

[Didayolo]

Description

Recent change in docker-compose.yml made the image build only for django and not site_worker (#2200).

On CircleCI, if tries to pull it instead of using the previously built image, it leads to a failure:

WARN[0000] The "RABBITMQ_HTTP_PROXY" variable is not set. Defaulting to a blank string. 
WARN[0000] The "RABBITMQ_HTTPS_PROXY" variable is not set. Defaulting to a blank string. 
WARN[0000] The "RABBITMQ_NO_PROXY" variable is not set. Defaulting to a blank string. 
[+] Running 2/8
 ⠙ db Pulling            0.1s 
[+] Running 2/8g         0.1s 
 ⠹ db Pulling            0.2s 
[+] Running 2/8g         0.2s access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to t
 ⠸ db Pulling            0.3s 
[+] Running 3/17         0.3s access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to t
 ⠼ db [⠀⠀⠀⠀⠀⠀⠀⠀⠀] Pulling 0.3s ccess denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to t
 ⠼ minio Pulling      0.3s ll access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to t
 ⠼ redis Pulling      0.3s ll access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to t
 ✘ site_worker Error  pull access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to the resource is denied0.1s   pull access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to t
 ✘ createbuckets Error Head "https://registry-1.docker.io/v2/minio/mc/manifests/RELEASE.2025-07-21T05-28-08Z": received unexpected HTTP status: 503 Service Temporarily Unavailable0.3s 
 ! django Warning     pull access denied for django_site-worker, repository does not exist or may require 'docker login': denied: requested access to the resource is denied0.1s 
 ⠸ caddy Pulling      0.3s 
 ⠸ flower Pulling     0.3s 
Error response from daemon: Head "https://registry-1.docker.io/v2/minio/mc/manifests/RELEASE.2025-07-21T05-28-08Z": received unexpected HTTP status: 503 Service Temporarily Unavailable

Exited with code exit status 1

By fixing pull_policy: never on site_worker we avoid this problem.

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• CircleCi tests are passing
• Ready to merge