Please upgrade c9s builders to an 8.4 or later kernel

This kernel version

Linux ppc64le-01.stream.rdu2.redhat.com 4.18.0-240.15.1.el8_3.ppc64le #1 SMP Tue Mar 2 15:24:24 UTC 2021 ppc64le ppc64le ppc64le GNU/Linux

lacks the scheduler fixes from bug 1877360 to avoid a broken rseq implementation. Now that we are going to enable rseq by default in 9, this might impact package builds. I don't think this will block anything, there will just be avoidable test suite failures.