GH-875: [CI] Bump default Python version on .env so dependencies like archery are installable on CI

[raulcd]

What's Changed

Update .env Python version that is used on the underlying docker images so it's compatible with minimum Python version for PyArrow/Archery.

Python 3.9 will be EOL on the next days.

Closes #875

[raulcd]

For the linux failures it seems pygit2 is building from sdist but I am unsure why, from my understanding it should use (in the x86_64 case) the:
pygit2-1.18.2-cp312-cp312-manylinux_2_26_x86_64.manylinux_2_28_x86_64.whl which is: manylinux: glibc 2.26+ x86-64manylinux: glibc 2.28+ x86-64 otherwise it fails building.

[lidavidm]

I think @jbonofre was also trying this in #865

[lidavidm]

  Building wheels for collected packages: pygit2, pandas

so both pygit2 and pandas.

We could run the image locally and then use pip to tell us what platform tags are supported. Isn't the base image for that intentionally kind of low?

[jbonofre]

It's already done in #876

[jbonofre]

I close this one in favor of #865

[raulcd]

Thanks! sounds good to me! I'll keep an eye on #865