Fix an issue in the GitDirectory loop when trying to commit without any actual changes

[silenceshell]

I have met an error when using gitops. Here are the steps to reproduce the error.

1. create a github repo and use ignited to watch the repo
2. add a yaml file like gitops sample code to git repo
3. ignited creates a new vm, and update the yaml and commit&push to git
4. in the git repo dir, update the yaml, change the diskSize to 4GB, and git add&commit&push to master branch
5. ignited do updated the vm, but it exits.

here is the log when ignited exits:

INFO[0214] New commit observed on branch "master": 32979b36abdbadd445fd949f4442728ef8eed5a0. User initiated: true
FATA[0215] The GitOps commit loop terminated with an error git commit and/or push error: no changes made in repo

There is nothing to commit, but ignited still try to commit and push, and caused the error.

I think the code below maybe is the spot:

func (d *GitDirectory) commitLoop() error {
...
		files, err := d.checkout.ChangedFiles(context.Background(), d. branch)

It equals to git diff --name-only --diff-filter=ACMRT master --. In the tmp dir like /tmp/flux-working259394949, this command always output git-vm.yaml, no matter I update the yaml file or not.

Is it better to use d.lastCommit as ref? It do fix my problem.

[luxas]

Thanks very much for this change!
Very appreciated

LGTM 👍