fix(utils): wrong ToTokens impl of the window proxy_url config (#9691)

Author: lucasfernog

.changes/fix-proxy-url-totokens-impl.md

@@ -0,0 +1,5 @@
+---
+"tauri-utils": patch:bug
+---
+
+Fixes the ToTokens implementation of the window configuration `proxy_url` field.

core/tauri-utils/src/config.rs

@@ -2243,7 +2243,7 @@ mod build {
       let minimizable = self.minimizable;
       let closable = self.closable;
       let title = str_lit(&self.title);
-      let proxy_url = opt_str_lit(self.proxy_url.as_ref());
+      let proxy_url = opt_lit(self.proxy_url.as_ref().map(url_lit).as_ref());
       let fullscreen = self.fullscreen;
       let focus = self.focus;
       let transparent = self.transparent;