Build SDL3 for ReadTheDocs workflow

Author: HexDecimal

.readthedocs.yaml

@@ -10,6 +10,12 @@ build:
     python: "3.11"
   apt_packages:
     - libsdl3-dev
+  jobs:
+    post_build:
+      - git clone --depth 1 --branch release-3.2.16 https://github.com/libsdl-org/SDL.git sdl_repo
+      - cmake -S sdl_repo -B sdl_build
+      - cmake --build sdl_build --config Debug
+      - cmake --install sdl_build --config Release --prefix /
 
 submodules:
   include: all