style(python): fix flake8 warning on python 3.12

[no changelog]

Author: matejcik

python/src/trezorlib/debuglink.py

@@ -156,8 +156,8 @@ def visible_screen(self) -> str:
             ********************
             ICON_CANCEL, -, CONFIRM
         """
-        title_separator = f"\n{20*'-'}\n"
-        btn_separator = f"\n{20*'*'}\n"
+        title_separator = f"\n{20 * '-'}\n"
+        btn_separator = f"\n{20 * '*'}\n"
 
         visible = ""
         if self.title():