Pin the version of python-gitlab used in the scheduled report pipeline

What does this MR do and why?

The scheduled pipeline report is failing due to a change in python-gitlab package (new version from today v4.11.0) https://python-gitlab.readthedocs.io/en/stable/changelog.html#v4-11-0-2024-09-13

error:

/tmp #  python3 ./.gitlab/ci/scripts/pipelines_schedules_report.py 1
Traceback (most recent call last):
  File "/tmp/./.gitlab/ci/scripts/pipelines_schedules_report.py", line 9, in <module>
    import gitlab
  File "/usr/local/lib/python3.12/site-packages/gitlab/__init__.py", line 30, in <module>
    from gitlab.client import Gitlab, GitlabList, GraphQL  # noqa: F401
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/gitlab/client.py", line 1279, in <module>
    class GraphQL:
  File "/usr/local/lib/python3.12/site-packages/gitlab/client.py", line 1286, in GraphQL
    client: Optional[httpx.Client] = None,
                     ^^^^^
NameError: name 'httpx' is not defined

I haven't found a way to fix it properly.

This MR change the base image to use an image with the python-gitlab embeded and versionned to avoid future surprise due to the pip --upgrade