Dependabot don't update dependency for git-submodule

I enabled dependabot with git submodule. dependabot created a Pull Request then I replied @dependabot rebase.

But dependabot replied

Looks like this PR is already up-to-date with master! If you’d still like to recreate it from scratch, overwriting any edits, you can request @dependabot recreate .

I am sure the submodule is not up-to-date