krakenw: Ignore unusable Pyenv shims when searching for an applicable Python version

[NiklasRosenstein]

Our current implementation in the krakenw.common.findpython module already supports looking for applicable versions in $PYENV_ROOT/versions, but it's not unlikely that Pyenv shim matches the version constraint as that will be on the PATH and we check $PYENV_ROOT/versions last. Sometimes that shim may not be configured properly so it reports an error (e.g. python3.10.13 available but not configured or something like that), and we should ignore a finding where this happens.