Use `<nav>` instead of `<div>` in the global navbar (#23125) (#23533)

Backport #23125 by @delvh

Furthermore improved/deleted some comments in the template.
The appearance did not change.

Co-authored-by: delvh <leon@kske.dev>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

templates/base/head_navbar.tmpl

@@ -1,4 +1,4 @@
-<div class="ui container" id="navbar" role="navigation" aria-label="{{.locale.Tr "aria.navbar"}}">
+<nav class="ui container" id="navbar" aria-label="{{.locale.Tr "aria.navbar"}}">
 	{{$notificationUnreadCount := 0}}
 	{{if .IsSigned}}
 		{{if .NotificationUnreadCount}}{{$notificationUnreadCount = call .NotificationUnreadCount}}{{end}}
@@ -150,7 +150,7 @@
 				</div><!-- end content create new menu -->
 			</div><!-- end dropdown menu create new -->
 
-			<div class="ui dropdown jump item tooltip gt-mx-0" tabindex="-1" data-content="{{.locale.Tr "user_profile_and_more"}}">
+			<div class="ui dropdown jump item tooltip gt-mx-0" data-content="{{.locale.Tr "user_profile_and_more"}}">
 				<span class="text">
 					{{avatar $.Context .SignedUser 24 "tiny"}}
 					<span class="sr-only">{{.locale.Tr "user_profile_and_more"}}</span>
@@ -190,14 +190,14 @@
 
 						<a class="{{if .PageIsAdmin}}active {{end}}item" href="{{AppSubUrl}}/admin">
 							{{svg "octicon-server"}}
-							{{.locale.Tr "admin_panel"}}<!-- Admin Panel -->
+							{{.locale.Tr "admin_panel"}}
 						</a>
 					{{end}}
 
 					<div class="divider"></div>
 					<a class="item link-action" href data-url="{{AppSubUrl}}/user/logout" data-redirect="{{AppSubUrl}}/">
 						{{svg "octicon-sign-out"}}
-						{{.locale.Tr "sign_out"}}<!-- Sign Out -->
+						{{.locale.Tr "sign_out"}}
 					</a>
 				</div><!-- end content avatar menu -->
 			</div><!-- end dropdown avatar menu -->
@@ -213,6 +213,6 @@
 			<a class="item{{if .PageIsSignIn}} active{{end}}" rel="nofollow" href="{{AppSubUrl}}/user/login{{if not .PageIsSignIn}}?redirect_to={{.CurrentURL}}{{end}}">
 				{{svg "octicon-sign-in"}} {{.locale.Tr "sign_in"}}
 			</a>
-		</div><!-- end anonymous right menu -->
+		</div><!-- end anonymous user right menu -->
 	{{end}}
-</div>
+</nav>