fix: docker compose test job should check response status code

[sirk0]

Fix Docker Compose action to check the return code of the health endpoint

Note that the frontend always redirects to homepage in case of 404, so it is not easily possible to reproduce

Original job passing for backend 404: https://github.com/sirk0/full-stack-fastapi-template/actions/runs/25822796893/job/75868162681

Run curl http://localhost:8000/api/v1/utils/health-check-fail
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100    22  100    22    0     0  10045      0 --:--:-- --:--:-- --:--:-- 11000
{"detail":"Not Found"}

Modified job failing for backend 404: https://github.com/sirk0/full-stack-fastapi-template/actions/runs/25826553849/job/75881067711?pr=1

Run curl --fail http://localhost:8000/api/v1/utils/health-check-fail
  curl --fail http://localhost:8000/api/v1/utils/health-check-fail
  shell: /usr/bin/bash -e {0}
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
  0    22    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl: (22) The requested URL returned error: 404
Error: Process completed with exit code 22.