specifying processor architecture does not work reliable

[mrh1997]

When a specific processor architecture is requested which is not installed tox implicitly falls back to another installed interpreter of the same version. I.e. if envlist=py39-x86 is specified and only python3.9-64 is installed on the system instead of printing an error (or skipping the environment if skip_missing_interpreters = true was specified) tox will implicitly use python3.9-64.

Tested on: Windows 10 (64bit), Python 3.10, tox 3.25.0 as well as 3.27.0