Fix:the rounded corners of the folded file are not displayed correctly (#29953)

Fix:    [#29933](https://github.com/go-gitea/gitea/issues/29933)

**Before**

![image](https://github.com/go-gitea/gitea/assets/37935145/71ec80f6-5896-4e4a-b686-4d792c11ebe2)

**After**

![image](https://github.com/go-gitea/gitea/assets/37935145/81348a61-946a-4562-881d-8d873e50228f)

---------

Co-authored-by: silverwind <me@silverwind.io>
Conflicts:
	- web_src/css/modules/segment.css
	  Ported by adding the new selector with a larger radius,
          keeping the existing one with ours.
(cherry picked from commit 43122ca984e5c411cb87140e3bf2597489aab956)

web_src/css/modules/segment.css

@@ -72,6 +72,9 @@
 .ui.segments:not(.horizontal) > .segment:only-child {
   border-radius: 0.214285717rem;
 }
+.ui.segments:not(.horizontal) > .segment:has(~ .tw-hidden) { /* workaround issue with :last-child ignoring hidden elements */
+  border-radius: 0.28571429rem;
+}
 
 .ui.segments > .ui.segments {
   border-top: 1px solid var(--color-secondary);