Since 3.13, CPython is provided in 2 flavors: regular and
free-threaded, with the 't' suffix.
An incomplete prefix ending with '[0-9]t'
resolves only among versions that also end with '[0-9]t'
* Document listing available versions in the tutorial (#1677)
* Reflect 3.7.15's extended support
* Document using development head with Homebrew
* Structurize the Upgrading section
* Fix Pyenv-latest documentation