Shader Language: Fixes EXTRA_MATRIX undefined.

Fixes #15453.

drivers/gles3/shader_compiler_gles3.cpp

@@ -715,7 +715,7 @@ ShaderCompilerGLES3::ShaderCompilerGLES3() {
 
 	actions[VS::SHADER_CANVAS_ITEM].renames["WORLD_MATRIX"] = "modelview_matrix";
 	actions[VS::SHADER_CANVAS_ITEM].renames["PROJECTION_MATRIX"] = "projection_matrix";
-	actions[VS::SHADER_CANVAS_ITEM].renames["EXTRA_MATRIX"] == "extra_matrix";
+	actions[VS::SHADER_CANVAS_ITEM].renames["EXTRA_MATRIX"] = "extra_matrix";
 	actions[VS::SHADER_CANVAS_ITEM].renames["TIME"] = "time";
 	actions[VS::SHADER_CANVAS_ITEM].renames["AT_LIGHT_PASS"] = "at_light_pass";
 	actions[VS::SHADER_CANVAS_ITEM].renames["INSTANCE_CUSTOM"] = "instance_custom";