Prevent SVG shrinking (#25652) (#25669)

Backport https://github.com/go-gitea/gitea/pull/25652

This will prevent the most common cases of SVG shrinking because lack of
space. I evaluated multiple options and this seems to be the one with
the least impact in size and processing cost, so I went with it.

Unfortunately, CSS can not dynamically convert `16` obtained from
`attr()` to `16px`, or else a generic solution for all sizes would have
been possible. But a solution is [in

sight](https://developer.mozilla.org/en-US/docs/Web/CSS/attr#type-or-unit)
with `attr(width px)` but no browser supports it currently.

web_src/css/index.css

@@ -7,6 +7,7 @@
 @import "./modules/breadcrumb.css";
 @import "./modules/card.css";
 @import "./modules/comment.css";
+@import "./modules/svg.css";
 
 @import "./shared/issuelist.css";
 @import "./shared/milestone.css";