tests: Bluetooth: quick-fix to EATT reconfigure

This test is going away when #55976 is merged.

Add a sleep to work around this sequence of events:
- central establishes channels
- peripheral tries to establish channels, fails (max num reached)
- central (still thinking chans are valid) triggers reconfigure
- collision mitigation on the peripheral, triggering a disconnect
  of both sides
- channels are established again, but the reconfigure isn't
  triggered again
- devices wait forever for the reconfigure cb

Fixes #55912

Signed-off-by: Jonathan Rico <jonathan.rico@nordicsemi.no>