drop python<=3.7 support

[kloczek]

According to https://endoflife.date/python python 3.7 has been EOSed 27 Jun 2023. Filter all code over pyupgracde --py38-plus.

Fixes

A short description of what this PR does.

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[kloczek]

Any chance to merge this PR? 🤔

BTW I'v been trying to test results of pyupgracde --py39-plus and looks like after apply such patch pyetst fails. It would be good to prepare twilio code for coming in next few weeks python 3.8 EOS as well or report to pypugrade case that it messes with twilio code.