Use gitrepo.Repository instead of wikipath (#35398)

Now the wikipath will not be referenced directly.

modules/gitrepo/commitgraph.go

@@ -0,0 +1,14 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gitrepo
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/modules/git"
+)
+
+func WriteCommitGraph(ctx context.Context, repo Repository) error {
+	return git.WriteCommitGraph(ctx, repoPath(repo))
+}