Add: WindowDesc unit test to validate ini-key value.

ini-key must be present if WWT_DEFSIZEBOX or WWT_STICKYBOX is present.
This was previously enforced by a workflow, however that parsed the source
code with regex which turned out to be error-prone.

src/tests/CMakeLists.txt

@@ -5,4 +5,5 @@ add_test_files(
     strings_func.cpp
     test_main.cpp
     test_script_admin.cpp
+    test_window_desc.cpp
 )