samples: bluetooth: peripheral_uart: Increase the main stack size

This commit increases the size of the main stack for prj_minimal.
This fixes a stack overflow on boot.

Ref: NCSDK-21709

Signed-off-by: Marcin Jelinski <marcin.jelinski@nordicsemi.no>

samples/bluetooth/peripheral_uart/prj_minimal.conf

@@ -94,7 +94,7 @@ CONFIG_BT_HCI_TX_STACK_SIZE_WITH_PROMPT=y
 CONFIG_BT_HCI_TX_STACK_SIZE=640
 CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=512
 CONFIG_MPSL_WORK_STACK_SIZE=256
-CONFIG_MAIN_STACK_SIZE=640
+CONFIG_MAIN_STACK_SIZE=864
 CONFIG_IDLE_STACK_SIZE=128
 CONFIG_ISR_STACK_SIZE=1024
 CONFIG_BT_NUS_THREAD_STACK_SIZE=512