[Repository] Improve install plan ids job to ignore deleted files

[jpvajda]

Relates to: https://github.com/newrelic/newrelic-quickstarts/pull/794

Issue

A contributor was attempting to move a few quickstart configs from one directory to another and it look like the validate install plan ids job that's failing might be confused trying to read one of the files that was deleted in the PR. So to resolve this PR and merge it, we just ignored the failed check, as this was a case where a quickstart config was moved from one directory to another.

Expected

• We actually do want validate install plan ids to run through to completion rather than to error out in a way that's irrelevant.

Acceptance Criteria

• [ ] consider if this is an edge case that we haven't accounted for and to add a kind of "null check" that will effectively ignore deleted files, but allow the overall validation to take place on the rest of the PR. (i.e. When we ask the GitHub API what files are in a given PR, does it return deleted files in its response— if so, should our script know to ignore those deleted files rather than trying to read their contents and throwing an error that prevents the actual validation check we care about from proceeding)