align the busy indicator centered

this doesn't actually change anything visually because it lives inside
the layout anyway, but the code's intent is to have the indicator be its
implicit size and centered, not stretched out across the layout

samba/filepropertiesplugin/qml/ChangePassword.qml

@@ -122,8 +122,7 @@ Kirigami.OverlaySheet {
 
         QQC2.BusyIndicator {
             id: busyIndicator
-            Layout.fillWidth: true
-            Layout.fillHeight: true
+            Layout.alignment: Qt.AlignCenter
             visible: running
             running: passwordRoot.busy
         }