fix safe sending signals (spelling mistake)

os.pidfile_open should be os.pidfd_open.
This was not noticed as the linux kernel this software is tested on does
not support the required syscalls.
os.pidfile was replaced by os.open
as os.pidfd_open requires at least linux 5.3 and
signal.pidfd_send_signal requires at least linux 5.1.

see also 7483451577

ueberzug/query_windows.py

@@ -48,7 +48,7 @@ def send_signal_safe(own_pid, target_pid):
     """
     pidfile = None
     try:
-        pidfile = os.pidfile_open(target_pid)
+        pidfile = os.open(f'/proc/{target_pid}', os.O_DIRECTORY)
         if is_same_command(own_pid, target_pid):
             signal.pidfd_send_signal(pidfile, signal.SIGUSR1)
     except FileNotFoundError: