[nrf fromlist] tests: drivers: uart: uart_errors: Cleanup after nRF54LM20 rename

Remove duplicated test configuration after
nrf54l20pdk/nrf54l20/cpuxxx was renamed to
nrf54lm20dk/nrf54lm20a/cpuxxx.

Upstream PR #: 92901

Signed-off-by: Sebastian Głąb <[email protected]>

Author: nordic-segl

tests/drivers/uart/uart_errors/boards/nrf54l20pdk_nrf54l20_cpuapp.overlay

@@ -6,13 +6,13 @@ common:
   harness: ztest
   harness_config:
     fixture: gpio_loopback
+  timeout: 30
 tests:
   drivers.uart.uart_errors.int_driven:
     filter: CONFIG_SERIAL_SUPPORT_INTERRUPT
     platform_allow:
       - nrf54h20dk/nrf54h20/cpuapp
       - nrf54l15dk/nrf54l15/cpuapp
-      - nrf54l20pdk/nrf54l20/cpuapp
       - nrf54lm20dk/nrf54lm20a/cpuapp
       - nrf5340dk/nrf5340/cpuapp
       - ophelia4ev/nrf54l15/cpuapp
@@ -21,7 +21,6 @@ tests:
     platform_allow:
       - nrf54h20dk/nrf54h20/cpuapp
       - nrf54l15dk/nrf54l15/cpuapp
-      - nrf54l20pdk/nrf54l20/cpuapp
       - nrf54lm20dk/nrf54lm20a/cpuapp
       - nrf5340dk/nrf5340/cpuapp
       - ophelia4ev/nrf54l15/cpuapp