ipatests: Update the subca used in TestIPACommand::test_cacert_manage
    
    The above test is installing 2 Let's Encrypt certificates:
    the root ISRG Root X1 and a subca. The subca expired Oct 6 and needs to
    be replaced with a valid one, otherwise ipa-cacert-manage install
    refuses to install it.
    
    Fixes: https://pagure.io/freeipa/issue/9006
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>