Display only current budget to Managers printing investments

In the specs, some investment were missing a heading_id, thus creating
another unexpected budget

By explicitly setting the heading_id we can control better which
budgets are created in each test

app/views/management/budgets/print_investments.html.erb

@@ -1,12 +1,10 @@
 <table>
-<% @budgets.each do |budget| %>
-  <tr id="<%= dom_id(budget) %>">
-    <td><%= budget.name %></td>
-    <td><%= budget.translated_phase %></td>
+  <tr id="<%= dom_id(@budget) %>">
+    <td><%= @budget.name %></td>
+    <td><%= @budget.translated_phase %></td>
     <td align="right">
       <%= link_to t("management.budgets.print_investments"),
-        print_management_budget_investments_path(budget) %>
+        print_management_budget_investments_path(@budget) %>
     </td>
   </tr>
-<% end %>
 </table>