tests: drivers: uart: depend on SERIAL_SUPPORT_ASYNC for ASYNC test

Only build the async testcase for platforms
that support async operation.

Signed-off-by: Benjamin Valentin <[email protected]>

Author: benpicco

tests/drivers/uart/uart_async_api/testcase.yaml

@@ -1,5 +1,5 @@
 tests:
   peripheral.uart_async_api:
     tags: drivers
-    filter: CONFIG_UART_CONSOLE
+    filter: CONFIG_UART_CONSOLE and CONFIG_SERIAL_SUPPORT_ASYNC
     harness: keyboard