Fixed warnings in CI related to copying freetype dll on Windows

CMakeLists.txt

@@ -22,7 +22,7 @@
 
 # If the cmake version is higher than the minimum version then enable all new policies, up to the maximum version specified.
 # When cmake is newer than the highest version then its newest policies will still be set to the old behavior for compatibility.
-cmake_minimum_required(VERSION 3.16...3.29)
+cmake_minimum_required(VERSION 3.16...3.31)
 
 # Include macros such as tgui_set_option
 include(${CMAKE_CURRENT_SOURCE_DIR}/cmake/Macros.cmake)

cmake/Macros.cmake

@@ -129,8 +129,16 @@ function(copy_dlls_to_exe post_build_destination install_destination target)
             list(APPEND files_to_copy "$<TARGET_FILE:tgui>")
         endif()
 
-        # Copy the FreeType dll if needed and when we know where it is
+        # Copy the FreeType dll if needed and if we know where it is
         if(TGUI_HAS_FONT_BACKEND_FREETYPE AND FREETYPE_WINDOWS_BINARIES_PATH AND NOT TGUI_USE_STATIC_STD_LIBS)
+            # Turn backslashes into slashes on Windows, because the install() command can fail if the
+            # FREETYPE_WINDOWS_BINARIES_PATH variable was initialized with an environment variable that contains backslashes.
+            if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.20)
+                cmake_path(SET FREETYPE_WINDOWS_BINARIES_PATH "${FREETYPE_WINDOWS_BINARIES_PATH}")
+            else()
+                file(TO_CMAKE_PATH "${FREETYPE_WINDOWS_BINARIES_PATH}" FREETYPE_WINDOWS_BINARIES_PATH)
+            endif()
+
             if(CMAKE_SIZEOF_VOID_P EQUAL 8)
                 set(freetype_dll "${FREETYPE_WINDOWS_BINARIES_PATH}/release dll/win64/freetype.dll")
             else()