Show scrollbar only when needed (go-gitea#6802)

Author: lafriks

public/css/index.css

@@ -327,6 +327,10 @@
                 padding: 1em 2em 1em 2em;
             }
 
+            pre {
+                overflow: auto;
+            }
+
             .code-view {
                 * {
                     font-size: 12px;