Adjust cargo divider for resupply tonnage calculation

Increased the cargo divider from 250 to 300 to refine the tonnage allowance calculation. This change improves accuracy in resupply estimations, aligning it better with target values.

MekHQ/src/mekhq/campaign/mission/resupplyAndCaches/Resupply.java

@@ -208,7 +208,7 @@ private static int calculateTargetCargoTonnage(Campaign campaign, AtBContract co
         double tonnageAllowance = meanTonnage * Math.min(unitAllowance, unitCount);
 
         // This divider gives us our target value of 5t per average IS Company
-        final int CARGO_DIVIDER = 250;
+        final int CARGO_DIVIDER = 300;
 
         double adjustedTonnage = tonnageAllowance / CARGO_DIVIDER;