remove invalid excel worksheet characters

app/models/champs/repetition_champ.rb

@@ -36,7 +36,8 @@ class Champs::RepetitionChamp < Champ
   # We have to truncate the label here as spreadsheets have a (30 char) limit on length.
   def libelle_for_export
     str = "(#{type_de_champ.stable_id}) #{libelle}"
-    ActiveStorage::Filename.new(str).sanitized.truncate(30)
+    # /\*?[] are invalid Excel worksheet characters
+    ActiveStorage::Filename.new(str.delete('[]*?')).sanitized.truncate(30)
   end
 
   class Row < Hashie::Dash