Log all js exceptions to logfile with level warn.

Author: rasjani

src/SeleniumTestability/listener.py

@@ -129,4 +129,4 @@ def before_quit(self: "TestabilityListener", driver: WebDriver) -> None:
 
     @log_wrapper
     def on_exception(self: "TestabilityListener", exception: Exception, driver: WebDriver) -> None:
-        pass
+        self.logger.warn(str(exception))