Keep `Integrations Packages Tests` from failing sucessfully

[bunchesofdonald]

Pull requests that do not change the integrations will have the Integrations Packages Tests 'fail' while all the steps succeed. GitHub reports the failure with:

Error when evaluating 'strategy' for job 'run-tests'. .github/workflows/integration-package-tests.yaml (Line: 55, Col: 15): Matrix must define at least one vector

This adds an if to the prepare-matrix step to that double checks that the test-all-integrations label is added or changes to the integrations themselves has happened.