Vendor jquery.are-you-sure with strict mode fixes (#26901)

Extract from https://github.com/go-gitea/gitea/pull/25940 and because
https://github.com/go-gitea/gitea/pull/26743 does seem to need more
work.

This will be required if we are to run our JS in [strict
mode](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode).

Previously, the two variables `$fields` and `$dirtyForms` polluted
`window`:

<img width="1145" alt="image"
src="https://github.com/go-gitea/gitea/assets/115237/e0270a0e-b881-4ed7-9cc4-e9ab25c0a2bc">

package.json

@@ -26,7 +26,6 @@
     "escape-goat": "4.0.0",
     "fast-glob": "3.3.1",
     "jquery": "3.7.1",
-    "jquery.are-you-sure": "1.9.0",
     "katex": "0.16.8",
     "license-checker-webpack-plugin": "0.2.1",
     "lightningcss-loader": "2.1.0",