`tox config -e pyXX` gives useless results if `XX` is invalid

[stephenfin]

Issue

(note: Consider this very low-priority or even closeable. I'm mainly reporting it so there's a record of the behavior somewhere)

Contrast:

❯ tox -e py47 run
py47: skipped because could not find python interpreter with spec(s): py47
  py47: SKIP (0.00 seconds)
  evaluation failed :( (0.24 seconds)

❯ echo $?
255

With:

❯ tox -e py47 config
[testenv:py47]
type = VirtualEnvRunner
...
{snipped}
...
env_site_packages_dir = # Exception: RuntimeError("failed to find interpreter for Builtin discover of python_spec='py47'")
env_bin_dir = # Exception: RuntimeError("failed to find interpreter for Builtin discover of python_spec='py47'")
env_python = # Exception: RuntimeError("failed to find interpreter for Builtin discover of python_spec='py47'")
py_dot_ver = # Exception: Skip('could not find python interpreter with spec(s): py47')
py_impl = # Exception: Skip('could not find python interpreter with spec(s): py47')
py_free_threaded = # Exception: Skip('could not find python interpreter with spec(s): py47')
...
{snipped}
...
wheel_build_env = # Exception: Skip('could not find python interpreter with spec(s): py47')

❯ echo $?
0

I suspect we want the latter to at least return an error code. This happens if py isn't part of any factor:

❯ tox -e foobar config
ROOT: HandledError| provided environments not found in configuration file:
foobar

❯ echo $?
254

Environment

Irrelevant.

Output of running tox

❯ tox --version
4.32.0 from /usr/lib/python3.14/site-packages/tox/__init__.py

Minimal example

See above.