Update SDL to 2.28.1

The latest version fixes SDL's rendering error.
Closes #131

Author: HexDecimal

CHANGELOG.md

@@ -6,6 +6,11 @@ This project adheres to [Semantic Versioning](https://semver.org/) since version
 ## [Unreleased]
 ### Changed
 - Added an empty `__slots__` to `EventDispatch`.
+- Bundle `SDL 2.28.1` on Windows and MacOS.
+
+### Fixed
+- Fixed "SDL failed to get a vertex buffer for this Direct3D 9 rendering batch!"
+  https://github.com/libtcod/python-tcod/issues/131
 
 ### Removed
 - Dropped support for Python 3.7.

build_sdl.py

@@ -26,7 +26,7 @@
 # The SDL2 version to parse and export symbols from.
 SDL2_PARSE_VERSION = os.environ.get("SDL_VERSION", "2.0.20")
 # The SDL2 version to include in binary distributions.
-SDL2_BUNDLE_VERSION = os.environ.get("SDL_VERSION", "2.26.0")
+SDL2_BUNDLE_VERSION = os.environ.get("SDL_VERSION", "2.28.1")
 
 
 # Used to remove excessive newlines in debug outputs.