Geometry Nodes: Add boolean attribute in utility function

This follows up rBc484b54453e607, adding the boolean custom property
data type in one more place that was missed.

source/blender/nodes/intern/node_geometry_exec.cc

@@ -96,6 +96,9 @@ CustomDataType GeoNodeExecParams::get_input_attribute_data_type(
   if (found_socket->type == SOCK_RGBA) {
     return CD_PROP_COLOR;
   }
+  if (found_socket->type == SOCK_BOOLEAN) {
+    return CD_PROP_BOOL;
+  }
 
   BLI_assert(false);
   return default_type;