Nightly test: add +15min for test_ipahealthcheck
    
    The test test_ipahealthcheck.py::TestIpaHealthcheck frequently
    hits its 90min timeout. Extend by 15min to allow completion.
    
    Fixes: https://pagure.io/freeipa/issue/9362
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Anuja More <amore@redhat.com>