[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

tests/unit/channel_test.py

@@ -101,7 +101,7 @@ def test_send_signal(ssh_channel):
     ssh_channel.request_exec('bash -c \'trap "exit 1" SIGUSR1; echo ready; sleep 5; exit 0\'')
 
     # Wait until the process is ready to receive signal
-    data = ""
+    data = ''
     while not data.startswith('ready'):
         ssh_channel.poll(timeout=1000)
         data += ssh_channel.recv().decode('utf-8')