build: fix GN build of uv

PR-URL: https://github.com/nodejs/node/pull/56955
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Juan José Arboleda <soyjuanarbol@gmail.com>

deps/uv/unofficial.gni

@@ -90,7 +90,7 @@ template("uv_gn_build") {
       ldflags = [ "-pthread" ]
     }
     if (is_linux) {
-      libs += [
+      libs = [
         "m",
         "dl",
         "rt",