CMake should always test minimum SDL3 version

[madebr]

The SDL3 version is currently not tested when using SDL3 and SDL3_image as git submodules.

The following should be disallowed (because SDL3 is too old):

cmake_minimum_required(VERSION 3.20)
project(mygame C)

add_subdirectory(SDL3-3.1.6 EXCLUDE_FROM_ALL)
add_subdirectory(SDL3_image-3.2.4 EXCLUDE_FROM_ALL)

add_executable(mygame WIN32 main.c)
target_link_libraries(mygame  PRIVATE SDL3_image::SDL3_image SDL3::SDL3)

(this also applies to SDL3_mixer, SDL3_ttf and SDL3_net)