AppVeyor: Test EOL versions of CPython

[cclauss]

Run py --list to see which versions of Python are present.

• https://www.appveyor.com/docs/windows-images-software/#visual-studio-2019

$ py --list

 -V:3.12 *        Python 3.12 (64-bit)
 -V:3.12-32       Python 3.12 (32-bit)
 -V:3.11          Python 3.11 (64-bit)
 -V:3.11-32       Python 3.11 (32-bit)
 -V:3.10          Python 3.10 (64-bit)
 -V:3.10-32       Python 3.10 (32-bit)
 -V:3.9           Python 3.9 (64-bit)
 -V:3.9-32        Python 3.9 (32-bit)
 -V:3.8           Python 3.8 (64-bit)
 -V:3.8-32        Python 3.8 (32-bit)
 -V:3.7           Python 3.7 (64-bit)
 -V:3.7-32        Python 3.7 (32-bit)
 -V:2.7           Python 2.7
 -V:2.7-32        Python 2.7-32
 -V:2.6           Python 2.6
 -V:2.6-32        Python 2.6-32
 -V:ContinuumAnalytics/Anaconda38-64 Anaconda 4.8.2
 -V:ContinuumAnalytics/Anaconda37-32 Anaconda 4.8.2
 -V:ContinuumAnalytics/Anaconda37-64 Anaconda 4.8.2
 -V:ContinuumAnalytics/Anaconda36-32 Anaconda 4.5.4
 -V:ContinuumAnalytics/Anaconda36-64 Anaconda 4.5.4
 -V:ContinuumAnalytics/Anaconda35-32 Anaconda 4.2.12
 -V:ContinuumAnalytics/Anaconda35-64 Anaconda 4.2.12
 -V:ContinuumAnalytics/Anaconda27-32 Anaconda 4.7.12
 -V:ContinuumAnalytics/Anaconda27-64 Anaconda 4.7.12

[cclauss]

Closing in favor of #575