Bump SDL2 version (#4)

The previously used SDL 2.26.4 was released on march 7 2023

There are various relevant release notes since:
Fixed handling of third party PS4 controller input reports
Improved support for third-party Nintendo Switch controllers
... etc

engine/Makefile

@@ -85,7 +85,7 @@ ZLIBVER=1.3
 PNGVER=1.6.39
 OGGVER=1.3.4
 VORBISVER=1.3.6
-SDL2VER=2.26.4
+SDL2VER=2.30.4
 SCINTILLAVER=373
 OPUSVER=1.3.1
 SPEEXVER=1.2.0