update SDL3 to latest commit

libs/SDL3/test/testgpu/cube.glsl

@@ -0,0 +1,31 @@
+#version 450
+
+#ifdef VERTEX
+
+layout (location = 0) in vec3 in_position;
+layout (location = 1) in vec3 in_color;
+
+layout (location = 0) out vec4 out_color;
+
+layout (set = 1, binding = 0) uniform UBO
+{
+    mat4x4 modelViewProj;
+};
+
+void main()
+{
+    out_color = vec4(in_color, 1.0);
+    gl_Position = modelViewProj * vec4(in_position, 1.0);
+}
+
+#else
+
+layout (location = 0) in vec4 in_color;
+layout (location = 0) out vec4 out_color;
+
+void main()
+{
+    out_color = in_color;
+}
+
+#endif