Detecting rusdoc theme change fails with CSP

As mentioned in #1386 there is a CSP error from `storage-change-detection.html` having an inline script. This results in the header/footer not instantly updating when the theme in rustdoc changes, instead it updates after a page reload.

```
Content Security Policy: The page’s settings blocked the loading of a resource at inline (“default-src”). storage-change-detection.html:11:1
```