refactor: correct type hint

Co-authored-by: Heitor Lessa <heitor.lessa@hotmail.com>

Author: Michael Brewer

aws_lambda_powertools/metrics/base.py

@@ -185,7 +185,7 @@ def serialize_metric_set(self, metrics: Dict = None, dimensions: Dict = None, me
         logger.debug({"details": "Serializing metrics", "metrics": metrics, "dimensions": dimensions})
 
         metric_names_and_units: List[Dict[str, str]] = []  # [ { "Name": "metric_name", "Unit": "Count" } ]
-        metric_names_and_values: Dict[str, int] = {}  # { "metric_name": 1.0 }
+        metric_names_and_values: Dict[str, float] = {}  # { "metric_name": 1.0 }
 
         for metric_name in metrics:
             metric: dict = metrics[metric_name]