Fix UI regression of asciinema player (#26159) (#26162)

Backport #26159 by @wolfogre

It was caused by updating `asciinema-player`, the upstream changed the
CSS class prefix:
`https://github.com/asciinema/asciinema-player/commit/40505e479e8ba6833f178a3b7e85503c72491614`

<details>
<summary>Before:</summary>

<img width="1320" alt="image"
src="https://github.com/go-gitea/gitea/assets/9418365/b91a2cf5-c1da-43d6-bac2-bc278728b11e">

</details>


<details>
<summary>After:</summary>

<img width="1311" alt="image"
src="https://github.com/go-gitea/gitea/assets/9418365/c9872d25-e0bb-43d4-8b1e-d87c6b03c0a2">

</details>

Co-authored-by: Jason Song <i@wolfogre.com>

web_src/css/markup/asciicast.css

@@ -3,6 +3,6 @@
   height: auto;
 }
 
-.asciinema-terminal {
+.ap-terminal {
   overflow: hidden !important;
 }