spi_flash tests: Fix exclusion of new API tests in legacy mode

components/spi_flash/test/CMakeLists.txt

@@ -1,11 +1,15 @@
 set(src_dirs ".")
+set(exclude_srcs)
+
 if(IDF_TARGET STREQUAL "esp32")
     list(APPEND src_dirs "esp32")
+    if(CONFIG_SPI_FLASH_USE_LEGACY_IMPL)
+        set(exclude_srcs "esp32/test_esp_flash.c" "esp32/test_partition_ext.c")
+    endif()
 endif()
+
 idf_component_register(SRC_DIRS ${src_dirs}
+                       EXCLUDE_SRCS ${exclude_srcs}
                        INCLUDE_DIRS "."
                        REQUIRES unity test_utils spi_flash bootloader_support app_update)
 
-if(CONFIG_SPI_FLASH_USE_LEGACY_IMPL)
-    set(COMPONENT_SRCEXCLUDE "test_esp_flash.c" "test_partition_ext.c")
-endif()