Fix for GridSensor3D Warning: Cannot pass 1 as Enum "BaseMaterial3D.Transparency"

[Ivan-267]

Fixes the following warning by replacing the integer with the enum:

W 0:00:00:559   GDScript::reload: Cannot pass 1 as Enum "BaseMaterial3D.Transparency": no enum member has matching value.
  <GDScript Error>INT_AS_ENUM_WITHOUT_MATCH
  <GDScript Source>GridSensorStaticOnly3D.gd:100 @ GDScript::reload()

Checked with Godot 4.6.1.

Note: Filename in warning log doesn't match as I got the warning on a locally modified sensor with a different filename, but otherwise the fix matches.