[Linaro:ARM_CI] Prevent use of protobuf 4 on python 3.8
Hi Andrew,

Thanks for bringing this up! We have seen similar failure with that test on x86 as well. Since it is passing in other Python versions and because the immediately affected feature (DTensor) is experimental, we have [disabled](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/dtensor/python/tests/BUILD#L351) the test for the time being on Python 3.8. Can you do the same? @nitins17 https://github.com/tensorflow/tensorflow/pull/59664 #59664  has removed the need for this PR.
protobuf 4 can lead to segmentation faults on Python 3.8 so prevent that from happening by using protobuf 3 but only for Python 3.8

Fixes #59643 