[kokoro python] Set SDKROOT am: 79951829ae am: 908d775fbf am: 8fea86be29

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

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ia8519d53d011ec7562b5d85ea9182214a55d6ae2