fix(debug): Take into account parent handlers for debug logger (#4133)

We only check `logger.handlers` for existing handlers. This ignores any
potential parent handlers. By using `hasHandlers()`
([docs](https://docs.python.org/3/library/logging.html#logging.Logger.hasHandlers))
instead we take those into account as well.

Closes #3944

Author: sentrivana

sentry_sdk/debug.py

@@ -19,7 +19,7 @@ def filter(self, record):
 
 def init_debug_support():
     # type: () -> None
-    if not logger.handlers:
+    if not logger.hasHandlers():
         configure_logger()