Rollup merge of #122693 - ehuss:rust-css-header, r=GuillaumeGomez

Fix heading anchors in doc pages.

This fixes the heading anchors on the standalone doc pages (the index, releases, etc.) so that the § symbol is only shown when the user hovers over the heading. This was changed in rust-lang/rust#117662, but this CSS was not updated.

Author: matthiaskrgr