erp5_interface_post: update...

erp5_interface_post: update LetterPostModule_exportExportableLetterPostActivity with new workflow state name

bt5/erp5_interface_post/SkinTemplateItem/portal_skins/erp5_interface_post/LetterPostModule_exportExportableLetterPostActivity.py

 portal = context.getPortalObject()
 N_ = portal.Base_translateString
 
-letter_post_list = context.searchFolder(simulation_state='exportable')
+letter_post_list = context.searchFolder(simulation_state='export_prepared')
 merged_pdf_content = None
 
 for letter_post in letter_post_list: