Merge "Upgrade pybind11 to 'v2.6.1'" am: a6667bd8a7 am: b42141a814 am: 68d40b5a5f

Original change: https://android-review.googlesource.com/c/platform/external/python/pybind11/+/1550561

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Icc654ea901643b01b6a0483066c307e70bdb74a3