refactor!: remove go-git backend (#39487)

Removes the go-git backend so every build uses the git CLI backend. Its
Windows performance advantage is gone, it lacks SHA-256 support, and it
breaks repositories on Windows.

The performance changes moved to
https://github.com/go-gitea/gitea/pull/39526.

Fixes https://github.com/go-gitea/gitea/issues/38359
Fixes https://github.com/go-gitea/gitea/issues/34694

---------

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

modules/git/repo_base_test.go

@@ -0,0 +1,29 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestRepoCatFileBatch(t *testing.T) {
+	t.Run("MissingRepoAndClose", func(t *testing.T) {
+		testDir := filepath.Join(t.TempDir(), "testdir")
+		_ = os.Mkdir(testDir, 0o755)
+		repo, err := OpenRepositoryLocal(t.Context(), testDir)
+		require.NoError(t, err)
+		// when the repo is missing (it usually occurs during testing because the fixtures are synced frequently)
+		err = os.Remove(testDir)
+		require.NoError(t, err)
+		_, _, err = repo.CatFileBatch()
+		require.Error(t, err)
+		require.NoError(t, repo.Close()) // shouldn't panic
+	})
+
+	// TODO: test more methods and concurrency queries
+}