fix: remove empty git submodule app

[chamini2]

Getting error during git checkout in Github Actions

https://github.com/fal-ai/fal/actions/runs/3679701850/jobs/6228127484#step:3:128

::group::Setting up auth
Setting up auth
  /usr/bin/git config --local --name-only --get-regexp core\.sshCommand
  /usr/bin/git submodule foreach --recursive git config --local --name-only --get-regexp 'core\.sshCommand' && git config --local --unset-all 'core.sshCommand' || :
  Error: fatal: No url found for submodule path 'app' in .gitmodules
  ##[debug]Unsetting HOME override
  ::remove-matcher owner=checkout-git::
  ##[debug]Removed matchers: 'checkout-git'
  Error: The process '/usr/bin/git' failed with exit code 128
  ##[debug]Node Action run completed with exit code 1

Fix from actions/checkout#354

[chamini2]

It was added in https://github.com/fal-ai/fal/pull/682, we have to review if this happens in the next release?