gitlab-ci: Bump docker image

Bizarrely, the nixos/nix:2.3 tag still pointed to an image that is over two years old, while nixos/nix:2.3.13 is much newer. Use the latter.

Fixes #35 (closed), where the nixos image was too old to include the new Let's Encrypt certificate.

ci/config.sh

@@ -82,6 +82,10 @@ case $version in
     #       package                   ticket
     broken  "Agda"                    20294
     broken  "diagrams-core"           20539
+    broken  "inj-base"                20584
+    broken  "lens"                    20584
+    broken  "microlens"               20584
+    broken  "mono-traversable"        20584
     ;;
 
   *)
@@ -93,14 +97,14 @@ esac
 # ==============
 #
 # These are packages which we don't have patches for but want to test anyways.
-extra_package lens
+extra_package lens 5.0.1
 extra_package aeson 1.5.6.0
 extra_package criterion
 extra_package scotty
 extra_package generic-lens 2.2.0.0
 extra_package microstache
-extra_package singletons
-extra_package servant
+extra_package singletons 3.0
+extra_package servant 0.18.3
 extra_package hgmp
 extra_package Agda 2.6.1.3
 extra_package mmark