make writing main test easier (#27270)

This PR removed `unittest.MainTest` the second parameter
`TestOptions.GiteaRoot`. Now it detects the root directory by current
working directory.

---------

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

services/gitdiff/main_test.go

@@ -4,7 +4,6 @@
 package gitdiff
 
 import (
-	"path/filepath"
 	"testing"
 
 	"code.gitea.io/gitea/models/unittest"
@@ -15,7 +14,5 @@ import (
 )
 
 func TestMain(m *testing.M) {
-	unittest.MainTest(m, &unittest.TestOptions{
-		GiteaRootPath: filepath.Join("..", ".."),
-	})
+	unittest.MainTest(m)
 }