fix: in KHR_techniques_webgl, premultiplyAlpha of material default value should be false

Author: 06wj

src/loader/GLTFExtensions.js

@@ -420,10 +420,11 @@ export const KHR_techniques_webgl = {
             needBasicUnifroms: false,
             needBasicAttributes: false,
             useHeaderCache: true,
+            premultiplyAlpha: false,
             vs: vertexText,
             fs: fragmentText,
             attributes,
-            uniforms
+            uniforms,
         });
 
         if (info.premultiplyAlpha !== undefined) {