tests: lib: cpp: exclude nRF54L15

Exclude nRF54L15 from possible targets as its HAL
is incompatible with C++98.

Signed-off-by: Magdalena Pastula <magdalena.pastula@nordicsemi.no>

tests/lib/cpp/cxx/testcase.yaml

@@ -34,6 +34,8 @@ tests:
   # -std=c++98)
   cpp.main.cpp98:
     arch_exclude: posix
+    # Exclude nRF54L15 as its HAL is not compatible with C++98.
+    platform_exclude: nrf54l15pdk_nrf54l15_cpuapp
     build_only: true
     extra_configs:
       - CONFIG_STD_CPP98=y