Only run integration reports on PRs and commits that contain changes to `schemas` directory

[acmiyaguchi]

The current dataops-ci-bot is too noisy, and reports results on changes that are irrelevant to schema validation of the document sample. This could be reduced by checking the PR for changes to files under the schemas/ or templates directory.

This would be tested directly within the PR.

[acmiyaguchi]

Easiest way to get around this is to make PRs from a forked repository.