Fix Safari spinner rendering (#29801) (#29802)

Backport #29801 by @silverwind

Fixes: https://github.com/go-gitea/gitea/issues/29041
Fixes: https://github.com/go-gitea/gitea/pull/29713

Any of the `width: *-content` properties seem to workaround this Webkit
bug, this one seemed most suitable.

Before:
<img width="184" alt="Screenshot 2024-03-14 at 22 29 58"
src="https://github.com/go-gitea/gitea/assets/115237/6effc5f0-bc64-4752-be74-9c43b3974407">

After:
<img width="177" alt="Screenshot 2024-03-14 at 22 30 30"
src="https://github.com/go-gitea/gitea/assets/115237/5de244d7-6b46-428e-957c-4b10f53e2441">

Co-authored-by: silverwind <me@silverwind.io>

web_src/css/modules/animations.css

@@ -20,6 +20,7 @@
   left: 50%;
   top: 50%;
   height: min(4em, 66.6%);
+  width: fit-content; /* compat: safari - https://bugs.webkit.org/show_bug.cgi?id=267625 */
   aspect-ratio: 1;
   transform: translate(-50%, -50%);
   animation: isloadingspin 1000ms infinite linear;