Fix the grainy sky while using debanding

drivers/gles3/shaders/sky.glsl

@@ -215,6 +215,6 @@ void main() {
 	frag_color.a = alpha;
 
 #ifdef USE_DEBANDING
-	frag_color.rgb += interleaved_gradient_noise(gl_FragCoord.xy);
+	frag_color.rgb += interleaved_gradient_noise(gl_FragCoord.xy) * luminance_multiplier;
 #endif
 }

servers/rendering/renderer_rd/shaders/environment/sky.glsl

@@ -290,6 +290,6 @@ void main() {
 	}
 
 #ifdef USE_DEBANDING
-	frag_color.rgb += interleaved_gradient_noise(gl_FragCoord.xy);
+	frag_color.rgb += interleaved_gradient_noise(gl_FragCoord.xy) * params.luminance_multiplier;
 #endif
 }