[FIX] account: bank statement with many AML

- Create a bank statement with more than 80 lines (therefore more than
  80 AML)
- Reconcile the lines
- Go back to the bank statement, and try to add a new line

An error arise:
"You cannot do this modification on a posted journal entry, you can just
change some non legal fields"

The error arise on the `move_line_ids` field on which the web client
tries to write.

Actually, this field is hidden since it is only used in the domain of a
stat button. We can make it read-only.

opw-1921138

closes odoo/odoo#30266

addons/account/views/account_view.xml

@@ -559,7 +559,7 @@
                         <button class="oe_stat_button" name="button_journal_entries"
                                 string="Journal Entries" type="object"
                                 attrs="{'invisible':[('move_line_ids','=',[])]}" icon="fa-bars"/>
-                        <field name="move_line_ids" invisible="1"/>
+                        <field name="move_line_ids" invisible="1" readonly="1"/>
                     </div>
                     <div class="oe_title oe_inline">
                         <label for="name" class="oe_edit_only"/>