Cleanup: CMake: Fix cmake warning regarding DEPENDS keyword

DEPENDS is not supported for post_build commands and recent
cmake versions have started emitting warnings about that.

This can be safely removed, as cmake has been silently ignoring
the keyword for years.

build_files/cmake/testing.cmake

@@ -128,7 +128,6 @@ macro(blender_src_gtest_ex)
       if(WITH_WINDOWS_EXTERNAL_MANIFEST)
         add_custom_command(TARGET ${TARGET_NAME} POST_BUILD
           COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_BINARY_DIR}/tests.exe.manifest ${TESTS_OUTPUT_DIR}/${TARGET_NAME}.exe.manifest
-          DEPENDS ${CMAKE_BINARY_DIR}/tests.exe.manifest
         )
       endif()
     endif()