Fix typo in XPath expression in Bulgarian tax form view

Corrected a typographical error in the XPath expression within the account_tax_views.xml file. This change ensures the proper insertion of the `l10n_bg_reverse_charge_vat` field in the advanced_booleans group.

l10n_bg_tax_admin/views/account_tax_views.xml

@@ -6,7 +6,7 @@
             <field name="model">account.tax</field>
             <field name="inherit_id" ref="account.view_tax_form"/>
             <field name="arch" type="xml">
-                <xpath expr="//group[@name='advanced_booleans'" position="inside">
+                <xpath expr="//group[@name='advanced_booleans']" position="inside">
                     <field name="l10n_bg_reverse_charge_vat"/>
                 </xpath>
             </field>