documentclass{beamer}
usepackage[english,russian]{babel}
usepackage[utf8]{inputenc}
usepackage{caption,ragged2e,enumerate}
usefonttheme{serif}
usetheme{metropolis}

makeatletter
renewcommand@biblabel[1]{#1.}
makeatother

setbeamertemplate{bibliography entry title}{}
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begin{document}

    begin{frame}[t,allowframebreaks]
    cite{Zim:07} cite{Dal:88}
    setbeamertemplate{bibliography item}[text]
    bibliographystyle{ugost2008}
    bibliography{bl}
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@Book{Zim:07,
  author   = {P. Zimbardo},
  title    = {Lucifer Effect Understanding How Good People Turn Evil [Текст]},
  year     = {2007},
  language = {russian},
}

@InBook{Dal:88,
  author   = {В.И. Даль},
  title    = {Толковый словарь живого Великорусского языка, том второй [Текст]},
  year     = {1881},
  language = {russian},
  pages    = {807},
}