Fix overflow in commit graph (#17947)

* Fix overflow in commit graph

Limit commit message to 50% width. This is rather crude but should work
for common use cases with not too-long author names.

Fixes: https://github.com/go-gitea/gitea/issues/17944

* Make it work with dynamic width

* use span

* use explicit none

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

web_src/less/features/gitgraph.less

@@ -137,6 +137,7 @@
     .author .ui.avatar.image {
       width: auto;
       height: 18px;
+      max-width: none;
     }
   }