Fix python-worker.js path construction

Corrects the path concatenation for python-worker.js by adding a missing slash, ensuring the worker script loads correctly regardless of the base URL format.

{{cookiecutter.out_dir}}/web/python.js

@@ -13,7 +13,7 @@ globalThis.jsConnect = async function (appId, args, dartOnMessage) {
     console.log(`Starting up Python worker: ${appId}, args: ${args}`);
     _apps[appId] = app;
     app.worker = new Worker((flet.entryPointBaseUrl.endsWith("/") ?
-        flet.entryPointBaseUrl.slice(0, -1) : flet.entryPointBaseUrl) + "python-worker.js");
+        flet.entryPointBaseUrl.slice(0, -1) : flet.entryPointBaseUrl) + "/python-worker.js");
 
     var error;
     app.worker.onmessage = (event) => {