pleroma: fix build with libxcrypt

pkgs/servers/pleroma/default.nix

···
 { lib, beamPackages
 , fetchFromGitHub, fetchFromGitLab
 , file, cmake
+, libxcrypt
 , nixosTests, writeText
 , ...
 }:
···
         postInstall = "mv $out/lib/erlang/lib/crypt-${version}/priv/{source,crypt}.so";
 
         beamDeps = with final; [ elixir_make ];
+
+        buildInputs = [ libxcrypt ];
       };
       web_push_encryption = beamPackages.buildMix rec {
         name = "web_push_encryption";