Remove italics style in bibliography, use only upright font shape

What should work for any bibliography style using either em (e.g., plain) or emph (e.g., plainnat) or the more basic itshape is to put the bibliography inside a group and to issue letitshapeupshape at the start of this group.

documentclass{article}

usepackage{filecontents}

begin{filecontents}{jobname.bib}
@book{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
}
end{filecontents}

begin{document}

nocite{*}

begingroup
letitshapeupshape

bibliographystyle{plain}
bibliography{jobname}

endgroup

end{document}

Based on the following answer: https://tex.stackexchange.com/a/296150

For biblatex, you can disable all emphasizing (italics) with the following:

makeatletter
renewrobustcmd*{mkbibemph}{}
protectedlongdefblx@imc@mkbibemph#1{#1}
makeatother