Decrease issue font size in project template (#28054)

I propose to decrease font size. 18 is too big and looks ugly, on
windows. 14 is on par with other elements and save a bit of space.

![image](https://github.com/go-gitea/gitea/assets/13328513/bc41f65d-8f48-4fd9-8e3b-d7a73967b0aa)

![image](https://github.com/go-gitea/gitea/assets/13328513/70e78919-9b9b-4f57-a491-d746ea59c048)

Co-authored-by: Nikolay Kobzarev <n.kobzarev@aeronavigator.ru>

web_src/css/repo/issue-card.css

@@ -16,6 +16,6 @@
 
 .issue-card-title {
   flex: 1;
-  font-size: 18px;
+  font-size: 14px;
   margin-left: 4px;
 }