Allow single-file changes from users with contributions in September

[MaggieFero]

Since the idea is to disincentivize spam PRs so that maintainers can focus on PRs that will help end users, and some PRs that only affect a single file are significant (like the one that will resolve this issue), you could reduce false positives by exempting single-file commits from contributors who also have Github contributions in September (before Hacktoberfest started).

The Github GraphQL API has a ContributionCalendarMonth object that could be used for this.