Update builtin-rules.md

Author: SirLynix

docs/api/description/builtin-rules.md

@@ -672,7 +672,7 @@ target("test")
     set_kind("binary")
     add_rules("utils.hlsl2spv", {bin2c = true})
     add_files("src/*.c")
-    add_files("src/*.hlsl", "src/*.hlsl")
+    add_files("src/*.hlsl")
     add_packages("directxshadercompiler")
 ```