append to PATH env var on Windows for CTest

CMakeLists.txt

# works for Unix, Windows, etc.
cmake_minimum_required(VERSION 3.22)
project(WindowsPath LANGUAGES C)

find_library(ZLIB REQUIRED)

add_executable(hello hello.c)
target_link_libraries(hello PRIVATE ZLIB::ZLIB)

add_test(NAME unit_hello COMMAND hello)
if(WIN32)
set_property(TEST unit_hello PROPERTY ENVIRONMENT_MODIFICATION "PATH=path_list_append:/path/to/dlls")
endif()

hello.c

#include "zlib.h"

int main(void) { return 0; }