Set LANG= for _spack_fn_exists (#5475)
Set LANG= for _spack_fn_exists (#5475)

type's output can be localized, causing the grep to fail.
lgarren/spack,TheTimmy/spack,mfherbst/spack,krafczyk/spack,iulian787/spack,LLNL/spack,iulian787/spack,EmreAtes/spack,matthiasdiener/spack,lgarren/spack,TheTimmy/spack,tmerrick1/spack,lgarren/spack,EmreAtes/spack,LLNL/spack,tmerrick1/spack,iulian787/spack,tmerrick1/spack,krafczyk/spack,TheTimmy/spack,lgarren/spack,krafczyk/spack,matthiasdiener/spack,LLNL/spack,mfherbst/spack,skosukhin/spack,EmreAtes/spack,TheTimmy/spack,skosukhin/spack,TheTimmy/spack,tmerrick1/spack,krafczyk/spack,iulian787/spack,mfherbst/spack,matthiasdiener/spack,tmerrick1/spack,skosukhin/spack,mfherbst/spack,LLNL/spack,skosukhin/spack,lgarren/spack,EmreAtes/spack,matthiasdiener/spack,mfherbst/spack,EmreAtes/spack,skosukhin/spack,matthiasdiener/spack,krafczyk/spack,LLNL/spack,iulian787/spack