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_test.go

@@ -82,3 +82,42 @@ func TestProject(t *testing.T) {
 
 	assert.True(t, projectFromDB.IsClosed)
 }
+
+func TestProjectsSort(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+
+	tests := []struct {
+		sortType string
+		wants    []int64
+	}{
+		{
+			sortType: "default",
+			wants:    []int64{1, 3, 2, 4},
+		},
+		{
+			sortType: "oldest",
+			wants:    []int64{4, 2, 3, 1},
+		},
+		{
+			sortType: "recentupdate",
+			wants:    []int64{1, 3, 2, 4},
+		},
+		{
+			sortType: "leastupdate",
+			wants:    []int64{4, 2, 3, 1},
+		},
+	}
+
+	for _, tt := range tests {
+		projects, count, err := FindProjects(db.DefaultContext, SearchOptions{
+			OrderBy: GetSearchOrderByBySortType(tt.sortType),
+		})
+		assert.NoError(t, err)
+		assert.EqualValues(t, int64(4), count)
+		if assert.Len(t, projects, 4) {
+			for i := range projects {
+				assert.EqualValues(t, tt.wants[i], projects[i].ID)
+			}
+		}
+	}
+}