Issue card improvements (#30687)

Fixes https://github.com/go-gitea/gitea/issues/30682 and does a few
improvements:

- Use gap instead of margin/padding
- Don't render empty image div
- Remove `right floated` class that did nothing

<img width="406" alt="Screenshot 2024-04-24 at 20 21 20"
src="https://github.com/go-gitea/gitea/assets/115237/2fa88707-c2c4-40df-aee7-a684c3097ed0">

---------

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

web_src/css/repo/issue-card.css

@@ -1,6 +1,7 @@
 .issue-card {
   display: flex;
   flex-direction: column;
+  gap: 4px;
   align-items: start;
   border-radius: var(--border-radius);
   padding: 8px 10px;
@@ -17,7 +18,6 @@
 .issue-card-title {
   flex: 1;
   font-size: 14px;
-  margin-left: 4px;
 }
 
 .issue-card.sortable-chosen .issue-card-title {