Fix incorrect oldest sort in project list (#25806) (#25835)

Backport #25806 by @yp05327

sort type `oldest` should be `Asc`.
Added a test for this.

I see we have `SearchOrderBy` in db model, but we are using many
different ways to define the sort type.
~Maybe we can improve this later.~
↑ Improved in this PR

Co-authored-by: yp05327 <576951401@qq.com>

models/project/project.go

@@ -196,7 +196,7 @@ type SearchOptions struct {
 	RepoID   int64
 	Page     int
 	IsClosed util.OptionalBool
-	SortType string
+	OrderBy  db.SearchOrderBy
 	Type     Type
 }
 
@@ -226,26 +226,28 @@ func CountProjects(ctx context.Context, opts SearchOptions) (int64, error) {
 	return db.GetEngine(ctx).Where(opts.toConds()).Count(new(Project))
 }
 
+func GetSearchOrderByBySortType(sortType string) db.SearchOrderBy {
+	switch sortType {
+	case "oldest":
+		return db.SearchOrderByOldest
+	case "recentupdate":
+		return db.SearchOrderByRecentUpdated
+	case "leastupdate":
+		return db.SearchOrderByLeastUpdated
+	default:
+		return db.SearchOrderByNewest
+	}
+}
+
 // FindProjects returns a list of all projects that have been created in the repository
 func FindProjects(ctx context.Context, opts SearchOptions) ([]*Project, int64, error) {
-	e := db.GetEngine(ctx).Where(opts.toConds())
+	e := db.GetEngine(ctx).Where(opts.toConds()).OrderBy(opts.OrderBy.String())
 	projects := make([]*Project, 0, setting.UI.IssuePagingNum)
 
 	if opts.Page > 0 {
 		e = e.Limit(setting.UI.IssuePagingNum, (opts.Page-1)*setting.UI.IssuePagingNum)
 	}
 
-	switch opts.SortType {
-	case "oldest":
-		e.Desc("created_unix")
-	case "recentupdate":
-		e.Desc("updated_unix")
-	case "leastupdate":
-		e.Asc("updated_unix")
-	default:
-		e.Asc("created_unix")
-	}
-
 	count, err := e.FindAndCount(&projects)
 	return projects, count, err
 }