Fix: Add files that are not tracked yet

[localheinz]

This PR

• adds files first, then checks if there's a change

Fixes #16.

[stefanzweifel]

lgtm 👍

Thanks for your contribution. Will tag a release in the next days.

[localheinz]

Thank you, @stefanzweifel!

[stefanzweifel]

I'm sorry. I had to revert the changes in fb3de05.

While testing the action in a test project of mine, the action didn't commit changes of existing files. It seems git diff --quiet --staged returns false for changes in existing files and doesn't execute git push.

I will see, how I can implement this without breaking the existing feature set. (Maybe I can somehow add a test suite with bats 🤔)

If you have any suggestions, feel free to mention them here.