Update Python to the latest minor version 3.9.6 in 14.3

Update Python to the latest minor version (3.9 or 3.10) in GitLab 14.0 while current minor version is 3.7 (!3274 (merged)).

• 3.4 to 3.7: !3274 (merged) in %12.0
• 2.x to 3.4: in %8.11

TODO

• Update Python to 3.9.6 !5547 (merged)