ci: replace black with ruff format

We use `ruff` anyway, so it is one less dependency.

deltachat-rpc-client/examples/echobot.py

@@ -4,6 +4,7 @@
 it will echo back any text send to it, it also will print to console all Delta Chat core events.
 Pass --help to the CLI to see available options.
 """
+
 from deltachat_rpc_client import events, run_bot_cli
 
 hooks = events.HookCollection()

deltachat-rpc-client/examples/echobot_advanced.py

@@ -3,6 +3,7 @@
 
 it will echo back any message that has non-empty text and also supports the /help command.
 """
+
 import logging
 import sys
 from threading import Thread

deltachat-rpc-client/examples/echobot_no_hooks.py

@@ -2,6 +2,7 @@
 """
 Example echo bot without using hooks
 """
+
 import logging
 import sys