inhibitShortcutsDialog: Don't override resource

PermissionStore's Set() method takes a complete permission
table, so when setting an app's permission, we are implicitly
removing all previously set entries for other apps.

Switch to the SetPermission() method which sets the permission
for a single app.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5937

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2504>

data/dbus-interfaces/org.freedesktop.impl.portal.PermissionStore.xml

@@ -13,6 +13,13 @@
       <arg name="app_permissions" type="a{sas}" direction="in"/>
       <arg name="data" type="v" direction="in"/>
     </method>
+    <method name="SetPermission">
+      <arg name='table' type='s' direction='in'/>
+      <arg name='create' type='b' direction='in'/>
+      <arg name='id' type='s' direction='in'/>
+      <arg name='app' type='s' direction='in'/>
+      <arg name='permissions' type='as' direction='in'/>
+    </method>
     <signal name="Changed">
       <arg name="table" type="s" direction="out"/>
       <arg name="id" type="s" direction="out"/>