psh: killing newly created sleep psh process causes strange behavior

[damianloew]

• Tested on ia32-generic qemu:
  
• Similar behaviour on armv7m7-imxrt106x target:
  

[damianloew]

Referring to Ubuntu 20.04, same actions causes some 'strange' behavior too (2 newly created processes are killed):

Waiting for confirmation if this issue can be closed.