Fix description of GOOGLE_FUNCTION_SOURCE env var
Fix description of GOOGLE_FUNCTION_SOURCE env var

PiperOrigin-RevId: 311140978
Change-Id: I03776fbf61ff74deeae2aa368c64232da2538195

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks