ci: ignore generated code in coverage build (#7585)
ci: ignore generated code in coverage build (#7585)

Ignore directories containing generated code.  This also ignores
some hand-written pieces like `integration_tests` and `samples`,
but we're not particularly interested in coverage data for those
either.
googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp