Investigate "Testing Corefiles" section not showing core file in CI

[peace-maker]

Run ulimit -a
real-time non-blocking time  (microseconds, -R) unlimited
core file size              (blocks, -c) 0
data seg size               (kbytes, -d) unlimited
scheduling priority                 (-e) 0
file size                   (blocks, -f) unlimited
pending signals                     (-i) 63938
max locked memory           (kbytes, -l) 8192
max memory size             (kbytes, -m) unlimited
open files                          (-n) 65536
pipe size                (512 bytes, -p) 8
POSIX message queues         (bytes, -q) 819200
real-time priority                  (-r) 0
stack size                  (kbytes, -s) 16384
cpu time                   (seconds, -t) unlimited
max user processes                  (-u) 63938
virtual memory              (kbytes, -v) unlimited
file locks                          (-x) unlimited
|/usr/lib/systemd/systemd-coredump %P %u %g %s %t 9223372036854775808 %h
0
/home/runner/work/_temp/b14c03a9-9992-49a7-bec4-45339905b54b.sh: line 5:  5327 Segmentation fault      (core dumped) sh -c 'kill -11 $$'
ls: cannot access './*core*': No such file or directory
ls: cannot access '/var/crash/*.crash': No such file or directory
ls: cannot access '/var/lib/apport/coredump/core*': No such file or directory

pwntools/.github/workflows/ci.yml

Lines 110 to 116 in 6748a78

	- name: Testing Corefiles
	run: |
	ulimit -a
	ulimit -c unlimited
	cat /proc/sys/kernel/core_pattern
	cat /proc/sys/kernel/core_uses_pid
	( cd $(mktemp -d); sh -c 'kill -11 $$' || true; ls -la ./*core* /var/crash/*.crash /var/lib/apport/coredump/core*) || true

I don't know what this is supposed to test, but I guess it should show the core file in one of the locations we look for in the CorefileFinder class. Support for systemd-coredump was added in #1181

The CI test should probably fail if it doesn't find the core file.