add v1.541 (Extreme)

shaders/gbuffers_skybasic.fsh

@@ -0,0 +1,5 @@
+#version 120
+
+void main() {
+	gl_FragData[0] = vec4(0.0, 0.0, 0.0, 1.0); //fill with zeros to avoid issues, alpha has to be set to 1.0 to fix an optifine issue in 1.17+ causing the sky to be black at certain angles.
+}