update SDL3 to 3.1.6.

Makefile

@@ -15,8 +15,7 @@ LOVE_REPOSITORY := https://github.com/love2d/love
 
 # Project branches (for git-based projects)
 LOVE_BRANCH := main
-SDL3_BRANCH := main
-SDL3_REV := 569691797da62387cabaa3c9bc5b033e8bbeb17e
+SDL3_BRANCH := preview-3.1.6
 LUAJIT_BRANCH := v2.1
 OPENAL_BRANCH := 1.23.1
 ZLIB_BRANCH := v1.3
@@ -83,8 +82,7 @@ endif
 override SDL3_PATH := SDL3-$(SDL3_BRANCH)
 
 $(SDL3_PATH)/CMakeLists.txt:
-	git clone --depth 4000 -b $(SDL3_BRANCH) https://github.com/libsdl-org/SDL $(SDL3_PATH)
-	cd $(SDL3_PATH) && git checkout $(SDL3_REV)
+	git clone --depth 1 -b $(SDL3_BRANCH) https://github.com/libsdl-org/SDL $(SDL3_PATH)
 
 $(SDL3_PATH)/build/CMakeCache.txt: $(CMAKE) $(SDL3_PATH)/CMakeLists.txt
 	$(CMAKE) -B$(SDL3_PATH)/build -S$(SDL3_PATH) $(CMAKE_OPTS)