Bumped python version to python3.10

Tobyrequested to merge
set-pyversion-as-variable into master

Version bumps:

  • python 3.7 -> 3.10
  • ci docker image 19.03.0 -> 20.10.16
  • pytest 4.6.2 -> 7.2.2
  • pymysql 0.9.3 -> 1.0.0
Edited by Toby

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