[Cython] Remove Py3.4 support in Cython 3.0?

[Stefan Behnel]

This should also have gone to cython-users (not just cython-devel), as it 
has the larger audience.

Stefan Behnel wrote:
> Hi,
> 
> I looked up where Python 3.4 is still being used.
> 
> Ubuntu 14.04 – EOS 2019, EOL April 2022
> Debian 8 – EOL
> Centos 6 – EOL
> 
> Later distribution versions have newer CPythons:
> 
> Ubuntu 16.04: Py3.5  (EOS April 2021, EOL 2024)
> Debian 9: Py3.5  (EOL June 2022)
> Centos 7: Py3.6  (EOL June 2024)
> 
> I think we can safely drop Py3.4 support already for Cython 3.0.
> 
> The advantage isn't big, since we still support Py2.7, but we can at least 
> stop testing it, and start relying on the Py3.5 C-API for Py3.
> 
> Given that Py3.5 is also going out of support in major Linux distributions 
> within a year's time, I'd suggest we drop support for it in Cython 3.1, 
> together with Py2 support, making the minimum version Py3.6. That would 
> mean that we can start using f-strings, dict ordering, and what not.
> 
> Any objections?
> 
> Stefan