accounting: fix permission of "Conversion" views of Internal Transactions

These actions should be always displayed, not only when user can modify,
otherwise the action is no longer displayed once the transaction
becomes delivered.

bt5/erp5_accounting/ActionTemplateItem/portal_types/Internal%20Invoice%20Transaction/destination_asset.xml

@@ -46,7 +46,7 @@
             <key> <string>permissions</string> </key>
             <value>
               <tuple>
-                <string>Modify portal content</string>
+                <string>View</string>
               </tuple>
             </value>
         </item>

bt5/erp5_accounting/ActionTemplateItem/portal_types/Internal%20Invoice%20Transaction/source_asset.xml

@@ -46,7 +46,7 @@
             <key> <string>permissions</string> </key>
             <value>
               <tuple>
-                <string>Modify portal content</string>
+                <string>View</string>
               </tuple>
             </value>
         </item>