test: fix retry thread cycling in _write_batching unit test

Author: karel-rehor

tests/test_influxdb_client_3.py

@@ -84,6 +84,8 @@ def test_write_api_custom_options_no_error(self):
             self.assertTrue(True)
         except Exception as e:
             self.fail(f"Write API with default options raised an exception: {str(e)}")
+        finally:
+            client._write_api._on_complete()  # abort batch writes - otherwise test cycles through urllib3 retries
 
     def test_default_client(self):
         expected_precision = DefaultWriteOptions.write_precision.value