chore: merge tests.AddFixtures and unittest.OverrideFixtures (#7648)

The only parameter that is ever used is a single directory, make it that only instead of a more complex option structure.

Remove tests.AddFixtures that was the simpler form because it is now redundant.

---

Backporting to v11.0 will help with automated backporting of bug fixes in need of custom made fixtures.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7648
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

models/auth/oauth2_test.go

@@ -4,14 +4,12 @@
 package auth_test
 
 import (
-	"path/filepath"
 	"slices"
 	"testing"
 
 	auth_model "forgejo.org/models/auth"
 	"forgejo.org/models/db"
 	"forgejo.org/models/unittest"
-	"forgejo.org/modules/setting"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -275,13 +273,7 @@ func TestBuiltinApplicationsClientIDs(t *testing.T) {
 }
 
 func TestOrphanedOAuth2Applications(t *testing.T) {
-	defer unittest.OverrideFixtures(
-		unittest.FixturesOptions{
-			Dir:  filepath.Join(setting.AppWorkPath, "models/fixtures/"),
-			Base: setting.AppWorkPath,
-			Dirs: []string{"models/auth/TestOrphanedOAuth2Applications/"},
-		},
-	)()
+	defer unittest.OverrideFixtures("models/auth/TestOrphanedOAuth2Applications")()
 	require.NoError(t, unittest.PrepareTestDatabase())
 
 	count, err := auth_model.CountOrphanedOAuth2Applications(db.DefaultContext)