ci/parse: test for nix 2.3 and lix

This adds the minimum nix version and the latest lix version to the
matrix of parse checks. Especially the minimum nix version is relevant,
because parsing routinely breaks because of introduction of newer
syntax.

Adding lix just completes the picture.

.github/workflows/nix-parse-v2.yml

@@ -27,4 +27,5 @@ jobs:
 
       - name: Parse all nix files
         run: |
-          nix-build ci -A parse
+          # Tests multiple versions at once, let's make sure all of them run, so keep-going.
+          nix-build ci -A parse --keep-going

ci/default.nix

@@ -78,6 +78,8 @@ in
   manual-nixpkgs-tests = (import ../pkgs/top-level/release.nix { }).manual.tests;
   parse = pkgs.lib.recurseIntoAttrs {
     latest = pkgs.callPackage ./parse.nix { nix = pkgs.nixVersions.latest; };
+    lix = pkgs.callPackage ./parse.nix { nix = pkgs.lix; };
+    minimum = pkgs.callPackage ./parse.nix { nix = pkgs.nixVersions.minimum; };
   };
   shell = import ../shell.nix { inherit nixpkgs system; };
 }