add only_third_party label to any PR with only third_party changes (#1202)
add only_third_party label to any PR with only third_party changes (#1202)

Merged PR #1202.

GoogleCloudPlatform/magic-modules,GoogleCloudPlatform/magic-modules,GoogleCloudPlatform/magic-modules,GoogleCloudPlatform/magic-modules,GoogleCloudPlatform/magic-modules