Use add_hash instead of set_hash in integration tests #374

As a preliminary work for #309 since set_array will change its behaviour but add_array will keep the functionality.

Author: TobiasNx

metafix/src/test/resources/org/metafacture/metafix/integration/method/fromXml/toJson/replace_toUpper/test.fix

@@ -1,5 +1,5 @@
 do list(path: "700[01] ", "var": "$i")
-  set_hash("contribution[].$append.agent")
+  add_hash("contribution[].$append.agent")
   copy_field("$i.a", "contribution[].$last.agent.label")
 end
 

metafix/src/test/resources/org/metafacture/metafix/integration/method/fromXml/toJson/replace_toUpperStrictnessHandlesProcessExceptions/test.fix

@@ -1,5 +1,5 @@
 do list(path: "700[01] ", "var": "$i")
-  set_hash("contribution[].$append.agent")
+  add_hash("contribution[].$append.agent")
   copy_field("$i.a", "contribution[].$last.agent.label")
 end