EI S11: Fixed units incorrectly costing upkeep after leveling up

(cherry-picked from commit d217dfc13c)

changelog.md

@@ -5,6 +5,7 @@
  ### Campaigns
    * Eastern Invasion
      * Fixed some Lua errors in S05.
+     * In 'Captured', fixed units incorrectly costing upkeep after leveling up.
    * Secrets of the Ancients
      * Fixed several inconsistently spelled names.
    * The Hammer of Thursagan

data/campaigns/Eastern_Invasion/scenarios/11_Captured.cfg

@@ -1279,6 +1279,27 @@
         [/endlevel]
     [/event]
 
+    [event]
+        name=post advance
+        first_time_only=no
+
+        [filter]
+            [filter_wml]
+                upkeep=full
+
+                [variables]
+                    temporary_free_upkeep=yes
+                [/variables]
+            [/filter_wml]
+        [/filter]
+
+        {VARIABLE unit.upkeep loyal}
+
+        [unstore_unit]
+            variable=unit
+        [/unstore_unit]
+    [/event]
+
     [event]
         name=victory