NR S2: let Hammel not take part in combat

All this trouble is about keeping him alive after all.
And fix a spelling mistake resuling in always false.

[ci skip]

data/campaigns/Northern_Rebirth/scenarios/02_01_Infested_Caves.cfg

@@ -110,6 +110,7 @@
             recruitment_pattern=fighter,fighter,fighter,mixed fighter
             grouping=defensive
             support_villages=yes
+            passive_leader=yes
             # in the unexpected case that they become too strong they should not clear the whole map
             [avoid]
                 x=1-31
@@ -778,7 +779,7 @@
         [/modify_side]
         [if]
             [variable]
-                name=turn_unmer
+                name=turn_number
                 greater_than=30
             [/variable]
             [then]