testing/ostest: set STACKSIZE for the standalone ELF build

The CMake build passed no STACKSIZE, so kernel-mode ELF loading fell
back to CONFIG_ELF_STACKSIZE, which may exceed the initial user heap.
Use CONFIG_DEFAULT_TASK_STACKSIZE as the Makefile does.

Signed-off-by: raiden00pl <raiden00@railab.me>
Assisted-by: Claude Code

Author: raiden00pl

testing/ostest/CMakeLists.txt

@@ -176,6 +176,7 @@ if(CONFIG_TESTING_OSTEST)
   endif()
 
   set(OSTEST_SRCS ostest_main.c ${SRCS})
-  nuttx_add_application(NAME ostest SRCS ${OSTEST_SRCS})
+  nuttx_add_application(NAME ostest SRCS ${OSTEST_SRCS} STACKSIZE
+                        ${CONFIG_DEFAULT_TASK_STACKSIZE})
 
 endif()