Pex-built tools may fail to run if built for a Python minor version for which the Pyenv shim errors

[NiklasRosenstein]

I'm unsure whether to report this on the Pex side, depends a bit on how we're building the Pex and point it to a Python minor version at the moment.

Basically, if you have Pyenv with a Python 3.10 version (for example) installed, but running python3.10 gives you something like this:

pyenv: python3.10: command not found

The `python3.10' command exists in these Python versions:
  3.10.14

Note: See 'pyenv help global' for tips on allowing both
      python2 and python3 to be found.

then the Pex-built binaries produced by Kraken may fail with the same error if they're targeting 3.10.

> :kraken-build:python.black.check PENDING
pyenv: python3.10: command not found

The `python3.10' command exists in these Python versions:
  3.10.14

Note: See 'pyenv help global' for tips on allowing both
      python2 and python3 to be found.
> :kraken-build:python.black.check FAILED