tests: drivers: uart: async_api: Add configuration for legacy nrf driver

Add configuration which tests legacy nrf uart driver.
Prevent tests on nrf52_bsim of the new driver (it is requiring
adjustments for the simulation). It will be fixed by another
patch.

Signed-off-by: Krzysztof Chruściński <[email protected]>

Author: nordic-krch

tests/drivers/uart/uart_async_api/testcase.yaml

@@ -13,6 +13,7 @@ tests:
     harness_config:
       fixture: gpio_loopback
     depends_on: gpio
+    tags: bsim_skip_CI
   drivers.uart.wide:
     filter: CONFIG_SERIAL_SUPPORT_ASYNC and not CONFIG_UART_MCUX_LPUART
     harness: ztest
@@ -25,6 +26,15 @@ tests:
     platform_allow: nucleo_h743zi
     integration_platforms:
       - nucleo_h743zi
+  drivers.uart.async_api.nrf_uarte_legacy:
+    platform_allow: nrf52840dk_nrf52840 nrf52_bsim
+    filter: CONFIG_SERIAL_SUPPORT_ASYNC
+    harness: ztest
+    harness_config:
+      fixture: gpio_loopback
+    depends_on: gpio
+    extra_configs:
+      - CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=y
   drivers.uart.async_api.nrf_uart:
     filter: CONFIG_SERIAL_SUPPORT_ASYNC
     harness: ztest