Confirmed on openssh-client 1:9.4p1-1, ssh-agent seems not going to pick its
dead children processes with wait(), no matter how they die. For example,
running `ssh-add -s /usr/lib/x86_64-linux-gnu/opensc-pkcs11.so` with a smart
card present will make ssh-agent spawn a ssh-pkcs11-helper to handle it, but
the child will always become a zombie without being wait(2)ed after it dies,
either terminating gracefully after running `ssh-add -e
/usr/lib/x86_64-linux-gnu/opensc-pkcs11.so`, or being kill(2)ed.
