Really fix __webpack_public_path__ for 1.11 (#11961)

Trailing slash is actually significant, fixed that and i've now tested
it as well.

Ref: #11839 (comment)

Author: silverwind

web_src/js/publicPath.js

@@ -3,7 +3,7 @@
 const { StaticUrlPrefix } = window.config;
 
 if (StaticUrlPrefix) {
-  __webpack_public_path__ = `${StaticUrlPrefix.endsWith('/') ? StaticUrlPrefix : `${StaticUrlPrefix}/`}js`;
+  __webpack_public_path__ = `${StaticUrlPrefix.endsWith('/') ? StaticUrlPrefix : `${StaticUrlPrefix}/`}js/`;
 } else if (document.currentScript && document.currentScript.src) {
   const url = new URL(document.currentScript.src);
   __webpack_public_path__ = `${url.pathname.replace(/\/[^/]*$/, '')}/`;