Upgrade Python from 3.7.8 to 3.7.9

Upgrade Python from 3.7.8 to 3.7.9.

Note about the future macOS Big Sur support

According to the changelog:

Additional fixes for testing on macOS 11 Big Sur Intel. Note: macOS 11 is not yet released, this release of Python is not fully supported on 11.0, and not all tests pass.

And the 3.7 branch will accept security fixes only until 2023 (doc), so there will be no more Windows installer nor features requests like the support for a new macOS version.