Replace call to deprecated method Thread.setDaemon()

This method was deprecated in Python 3.10, set the Thread.daemon
attribute directly instead.

See: python/cpython#25174

pifpaf/drivers/__init__.py

@@ -230,7 +230,7 @@ def _exec(self, command, stdout=False, ignore_failure=False,
             # Continue to read
             t = threading.Thread(target=self._read_in_bg,
                                  args=(app, c.pid, c.stdout,))
-            t.setDaemon(True)
+            t.daemon = True
             t.start()
             # Store the thread ref into the Process() to be able
             # to clean it