ci-fairy: explicitly specify get_all=False for fetching updated mrs

/usr/lib/python3.11/site-packages/ci_fairy.py:1902: UserWarning: Calling
    a `list()` method without specifying `get_all=True` or `iterator=True`
    will return a maximum of 100 items. Your query returned 100 of 579
    items. See
    https://python-gitlab.readthedocs.io/en/v4.5.0/api-usage.html#pagination
    for more details. If this was done intentionally, then this warning
    can be supressed by adding the argument `get_all=False` to the
    `list()` call.
    (python-gitlab: /usr/lib/python3.11/site-packages/ci_fairy.py:1902)

Checking the last 100 MRs is plenty enough, no need to iterate through all of them.

Closes #76