ci: update paths in a fuzzing workflow

Fuzzing is a heavyweight job, we can reduce a set of paths used for
triggering this job and therefore reduce an overall time of testing in
some cases.

The patch replaces `.github/workflows/**` to
`.github/workflows/fuzzing.yml` because workflows are independent and
changes in other workflows does not affect fuzzing at all and patch adds
Lua files (`**.lua`) to ignores because fuzzing focused on C/C++ code.

NO_CHANGELOG=ci
NO_DOC=ci
NO_TEST=ci