filter_shebang fails on non UTF-8 script

[cessenat]

Some typically European (Continental) scripts are in some variant of ISO-8859 which python knows as latin-1.
filter_shebang demands an UTF-8 input file so it fails for these scripts.
This is the case on package perl-tk with a copyright (©) character in ptked (Nick Ing-Simmons Copyright).
I made a proposal for modification in spack with PR 24263. It also traps some old Asian encoding.
I report this here following Massimiliano advise.

[alalazo]

@tgamblin I don't seem to have permissions to assign people, edit descriptions or attach labels in this repository, so for reference a link to the PR from which this issue originated spack/spack#24263

[tgamblin]

@alalazo try now -- should be fixed