[kokoro python] Set SDKROOT am: 79951829ae am: 908d775fbf

Original change: https://android-review.googlesource.com/c/platform/external/python/cpython3/+/1574220

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I66b87e8836020f5beaff727d52ca63fec94450c2