Fix ConfigLoggingUpdater not changing root logging level

Setting log level with method `logging.basicConfig` during
runtime is not working. Instead logging.getLogger() is used.

RELEASE_NOTES.md

@@ -14,4 +14,4 @@
 
 ## Bug Fixes
 
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
+* Fix bug with LoggingConfigUpdater not updating root logger level.

src/frequenz/sdk/config/_logging_config_updater.py

@@ -141,16 +141,24 @@ def __init__(
             config_recv: The receiver to listen for configuration changes.
             log_format: Use the specified format string in logs.
             log_datefmt: Use the specified date/time format in logs.
+
+        Note:
+            log_format and log_datefmt are passed to the `logging.basicConfig`
+            function. If any call to `logging.basicConfig` is made before this
+            actor is created, then this actor will not override it.
         """
         super().__init__()
         self._config_recv = config_recv
-        self._format = log_format
-        self._datefmt = log_datefmt
 
         # Setup default configuration.
         # This ensures logging is configured even if actor fails to start or
         # if the configuration cannot be loaded.
         self._current_config: LoggingConfig = LoggingConfig()
+
+        logging.basicConfig(
+            format=log_format,
+            datefmt=log_datefmt,
+        )
         self._update_logging(self._current_config)
 
     async def _run(self) -> None:
@@ -176,11 +184,10 @@ def _update_logging(self, config: LoggingConfig) -> None:
             logging.getLogger(logger_id).setLevel(logging.NOTSET)
 
         self._current_config = config
-        logging.basicConfig(
-            format=self._format,
-            level=self._current_config.root_logger.level,
-            datefmt=self._datefmt,
+        _logger.debug(
+            "Setting root logger level to '%s'", self._current_config.root_logger.level
         )
+        logging.getLogger().setLevel(self._current_config.root_logger.level)
 
         # For each logger in the new config, set the log level
         for logger_id, logger_config in self._current_config.loggers.items():