Declare fuel_type_battery

This itype was decentralized as part of commit 3799315, but my PR
for electric motors CleverRaven#38212 was made before that and needed
fuel_type_battery to be defined.

src/vehicle_move.cpp

@@ -39,6 +39,7 @@
 
 static const itype_id fuel_type_muscle( "muscle" );
 static const itype_id fuel_type_animal( "animal" );
+static const itype_id fuel_type_battery( "battery" );
 
 static const skill_id skill_driving( "driving" );