Force work challenge activity to be not resizable

We need to add the flag resizeableActivity to the root activity of
the task that holding the work challenge activity which is
ConfirmDeviceCredentialActivity$InternalActivity.

This activity is the entry point for work challenge and is not used
elsewhere.

Bug: 27565539

Change-Id: I79157e4ea9c7a52a1727919dcd4d311380492f3d