ipatests: fix test definition for test_trust
    
    The nightly test test_trust.py has been split into 2 jobs,
    one for test_trust.py::TestTrust (test_trust) and the other
    for the remaining test classes from the same file
    (test_trust_autoprivate).
    
    The backport forgot to narrow down the first job definition
    to the class test_trust.py::TestTrust in the 4-10_previous
    pipeline. Fix this omission.
    
    Related: https://pagure.io/freeipa/issue/9326
    Reviewed-By: Anuja More <amore@redhat.com>