fix #7623: ui: backup: only list guests of the selected pool

The guest list in the backup job editor filters the resource store by
the selected pool. With a plain string value, ExtJS matches any pool
that starts with it, ignoring case, so selecting 'Clients' also listed
the guests of 'Clients/Client1', 'Clients/Client2' and 'clients'.

The job itself only backs up the guests of the selected pool, so the
editor suggested that guests are covered which are not.

Match the pool id exactly and case-sensitively.

Signed-off-by: Michal Fox <me@dualfroz.com>

www/manager6/dc/Backup.js

@@ -124,6 +124,9 @@ Ext.define('PVE.dc.BackupEdit', {
                     id: 'poolFilter',
                     property: 'pool',
                     value: poolid,
+                    // a plain string filter would also match child pools like 'poolid/child'
+                    exactMatch: true,
+                    caseSensitive: true,
                 },
             ]);
             vmgrid.selModel.selectAll(true);