add self arg to ad_spend_parameters check

src/pysimmmulator/helpers.py

@@ -86,7 +86,7 @@ def __post_init__(self):
                 0 < v["max"] <= 1
             ), "Max spend must be between 0 and 1 for each channel"
 
-    def check(basic_params: basic_parameters):
+    def check(self, basic_params: basic_parameters):
         assert (
             len(self.max_min_proportion_on_each_channel.keys()) - 1
             == len(basic_params.all_channels)