templates: beamer: use new style texlive syntax

templates/beamer/flake.nix

@@ -3,12 +3,10 @@
 
   outputs = { self, dragnpkgs } @ inputs: dragnpkgs.lib.mkFlake {
     # Define a texlive environment to use
-    packages.texlive-custom = { texlive }: texlive.combine {
-      inherit (texlive)
-        scheme-medium
-        fontawesome5
-        moloch;
-    };
+    packages.texlive-custom = { texliveMedium }: texliveMedium.withPackages (ps: with ps; [
+      fontawesome5
+      moloch
+    ]);
 
     # Package definition for building the PDF
     packages.default = { system, stdenvNoCC }: stdenvNoCC.mkDerivation rec {