Ensure RSS icon is present on all repo tabs (#23904)

Previously, not all repo tabs had shown the RSS icon in the repo header
because the context data was not being set. Added this context data in a
new function.

Before:

<img width="806" alt="image"
src="https://user-images.githubusercontent.com/115237/229639615-9cc00e75-3a26-4ff4-a6f2-316c1fccc596.png">

After:

<img width="815" alt="Screenshot 2023-04-04 at 00 16 17"
src="https://user-images.githubusercontent.com/115237/229639201-2e1c015b-1f13-46d4-aa14-e7a82fab3982.png">

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/context/repo.go

@@ -537,6 +537,11 @@ func RepoAssignment(ctx *Context) (cancel context.CancelFunc) {
 	ctx.Data["RepoLink"] = ctx.Repo.RepoLink
 	ctx.Data["RepoRelPath"] = ctx.Repo.Owner.Name + "/" + ctx.Repo.Repository.Name
 
+	if setting.EnableFeed {
+		ctx.Data["EnableFeed"] = true
+		ctx.Data["FeedURL"] = ctx.Repo.RepoLink
+	}
+
 	unit, err := ctx.Repo.Repository.GetUnit(ctx, unit_model.TypeExternalTracker)
 	if err == nil {
 		ctx.Data["RepoExternalIssuesLink"] = unit.ExternalTrackerConfig().ExternalTrackerURL