Name experimental warning in PropertyLayer correctly

The experimental_warning_given variable in PropertyLayer was named incorrectly, probably while copying from the AgentSet. This commit fixes that.

Author: EwoutH

mesa/space.py

@@ -586,7 +586,7 @@ class PropertyLayer:
         aggregate_property(operation): Performs an aggregate operation over all cells.
     """
 
-    agentset_experimental_warning_given = False
+    propertylayer_experimental_warning_given = False
 
     def __init__(
         self, name: str, width: int, height: int, default_value, dtype=np.float64
@@ -633,14 +633,14 @@ def __init__(
 
         self.data = np.full((width, height), default_value, dtype=dtype)
 
-        if not self.__class__.agentset_experimental_warning_given:
+        if not self.__class__.propertylayer_experimental_warning_given:
             warnings.warn(
                 "The new PropertyLayer and _PropertyGrid classes experimental. It may be changed or removed in any and all future releases, including patch releases.\n"
                 "We would love to hear what you think about this new feature. If you have any thoughts, share them with us here: https://github.com/projectmesa/mesa/discussions/1932",
                 FutureWarning,
                 stacklevel=2,
             )
-            self.__class__.agentset_experimental_warning_given = True
+            self.__class__.propertylayer_experimental_warning_given = True
 
     def set_cell(self, position: Coordinate, value):
         """