fix ASF update action if there are no changes

[alexrashed]

Motivation

With https://github.com/localstack/localstack-ext/pull/2217, we changed to ruff which replaces a bunch of tools (flake8, isort, autoflake). Previously, these tools were directly called in the ASF scaffold and the result of the code generation was already perfectly formatted.
ruff cannot be called from Python code on in-memory strings, which is why we switched to our format-modified make target.
Turns out, the target does not work in case there are no changes (since then black does not get any input).
This PR slightly modifies the ASF update action such that this issue is prevented.

Changes

• Changes the ASF Update action such that the format-modified target is only executed if there are changes in the repo.

Testing

• We will execute the action from this branch. Since there currently no changes, this change is safe if the action run is successful.
  • https://github.com/localstack/localstack/actions/runs/6610132434/job/17951451836 💚

[dfangl]

Good catch!