Fix label list divider (go-gitea#25312)

We only needs 2 lines to hide the dividers.

```
  $dropdownLabelFilter.dropdown('setting', {'hideDividers': 'empty'});
  $dropdownLabelFilter.dropdown('refreshItems');
```

Other code blocks are refactored by the way.


![image](https://github.com/go-gitea/gitea/assets/2114189/74989996-fcea-4df4-b534-b06f7957939a)


![image](https://github.com/go-gitea/gitea/assets/2114189/ee3b3761-b96e-4fb5-b646-e9d3117e5f40)

Author: wxiaoguang

templates/repo/issue/list.tmpl

@@ -102,12 +102,13 @@
 								<input type="text" placeholder="{{.locale.Tr "repo.issues.filter_label"}}">
 							</div>
 							<span class="info">{{.locale.Tr "repo.issues.filter_label_exclude" | Safe}}</span>
+							<div class="ui divider"></div>
 							<a class="item" href="{{$.Link}}?q={{$.Keyword}}&type={{$.ViewType}}&sort={{$.SortType}}&state={{$.State}}&labels=0&milestone={{$.MilestoneID}}&project={{$.ProjectID}}&assignee={{$.AssigneeID}}&poster={{$.PosterID}}">{{.locale.Tr "repo.issues.filter_label_select_no_label"}}</a>
 							<a class="item" href="{{$.Link}}?q={{$.Keyword}}&type={{$.ViewType}}&sort={{$.SortType}}&state={{$.State}}&milestone={{$.MilestoneID}}&project={{$.ProjectID}}&assignee={{$.AssigneeID}}&poster={{$.PosterID}}">{{.locale.Tr "repo.issues.filter_label_no_select"}}</a>
 							{{$previousExclusiveScope := "_no_scope"}}
 							{{range .Labels}}
 								{{$exclusiveScope := .ExclusiveScope}}
-								{{if and (ne $previousExclusiveScope "_no_scope") (ne $previousExclusiveScope $exclusiveScope)}}
+								{{if and (ne $previousExclusiveScope $exclusiveScope)}}
 									<div class="ui divider"></div>
 								{{end}}
 								{{$previousExclusiveScope = $exclusiveScope}}

web_src/css/repo.css

@@ -149,7 +149,6 @@
 .repository .filter.menu.labels .label-filter .menu .info {
   display: inline-block;
   padding: 0.5rem 0.25rem;
-  border-bottom: 1px solid var(--color-secondary);
   font-size: 12px;
   width: 100%;
   white-space: nowrap;

web_src/js/features/repo-issue.js

@@ -149,6 +149,7 @@ export function initRepoIssueSidebarList() {
       }
     }
   });
+  $('.ui.dropdown.label-filter').dropdown('setting', {'hideDividers': 'empty'}).dropdown('refreshItems');
 }
 
 export function initRepoIssueCommentDelete() {