Update beam version from 2.29.0 to 2.31.0

[edualb]

Hello everyone, many people have been having a lot of exceptions with Beam version 2.29.0:

#281
StackOverflow
googleapis/google-cloud-java#3693

This PR has a goal to update Beam version 2.29.0 to 2.31.0 to solve these issues.

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[edualb]

@googlebot I signed it!

[prathapreddy123]

@edualb - Version upgrades are made by repo maintainers following beam releases. Flex templates (i.e v2/) has been upgraded to 2.31 and will upgrade classic templates as well shortly.