chore: still keep ctx in git.Repository struct for cat-file batch command (#38684)

Unfortunately, we can't completely remove the ctx from git.Repository,
because the CatFileBatch still heavily depends on a parent context.

If we remove the Repository ctx, the CatFileBatch will become a mess and
create a lot of unnecessary git processes.

http://localhost:3000/-/admin/monitor/perftrace

* Before: open a repo home, dozens of git processes (duplicate cat-file)
* After: only a few (no duplicate cat-file)

routers/web/repo/editor_test.go

@@ -21,7 +21,7 @@ func TestEditorUtils(t *testing.T) {
 		assert.Equal(t, "user2-patch-1", branchName)
 	})
 	t.Run("getClosestParentWithFiles", func(t *testing.T) {
-		gitRepo, _ := git.OpenRepository(repo)
+		gitRepo, _ := git.OpenRepository(t.Context(), repo)
 		defer gitRepo.Close()
 		treePath := getClosestParentWithFiles(t.Context(), gitRepo, "sub-home-md-img-check", "docs/foo/bar")
 		assert.Equal(t, "docs", treePath)