v0.171.0

Improvements to pre-commit github action dylanbannon (#365)

what

• triggering on labeling/unlabeling events
• handling the edge case where multiple terraform/[version] labels are assigned to a PR
• handling the case where a PR does not require a terraform/[version] label because it hs no modified .tf files

why

• Often, a PR will be ready to go except for failing pre-commit checks. It'd be nice to just be able to add a label in order to get the checks to pass, instead of having to add a label and then push a trivial commit.
• It's possible that someone might accidentally add multiple terraform/[version] labels to a PR. Previously, the behavior in this case was undefined. Now, it will return an informative error. (Also, now improperly formatted terraform/[version] labels will return a more informative error message.)
• There are many PRs for this repo that don't touch Terraform code. We shouldn't insist that they choose an arbitrary terraform/[version] label just to get their pre-commit checks to pass.