pandoc: provide matching version of skylighting{,-core}

Since 500b36d057ceaa7ad3e2e282958a44ed607b021f, there is a more recent
version of skylighting and skylighting-core available than Stackage LTS
contains. We'll have to manually provide matching versions for pandoc
3.1.6 again.

pkgs/development/haskell-modules/configuration-common.nix

···
       # pandoc depends on http-client-tls, which only starts depending
       # on crypton-connection in http-client-tls-0.3.6.2.
       http-client-tls = self.http-client-tls_0_3_6_2;
+
+      # pandoc and skylighting are developed in tandem
+      skylighting-core = self.skylighting-core_0_13_4_1;
+      skylighting = self.skylighting_0_13_4_1;
     };
   in {
     pandoc-cli = super.pandoc-cli.overrideScope pandoc-cli-overlay;