lib/tests: Also run with nixVersions.minimum and nixVersions.unstable

The previous commits ensure that the tests also succeed with those
versions

lib/tests/release.nix

@@ -2,9 +2,12 @@
   # Don't test properties of pkgs.lib, but rather the lib in the parent directory
   pkgs ? import ../.. {} // { lib = throw "pkgs.lib accessed, but the lib tests should use nixpkgs' lib path directly!"; },
   nix ? pkgs.nix,
+  nixVersions ? [ pkgs.nixVersions.minimum nix pkgs.nixVersions.unstable ],
 }:
 
-pkgs.runCommand "nixpkgs-lib-tests" {
+let
+  testWithNix = nix:
+    pkgs.runCommand "nixpkgs-lib-tests-nix-${nix.version}" {
       buildInputs = [
         (import ./check-eval.nix)
         (import ./maintainers.nix {
@@ -23,7 +26,7 @@ pkgs.runCommand "nixpkgs-lib-tests" {
         nix
       ];
       strictDeps = true;
-} ''
+    } ''
       datadir="${nix}/share"
       export TEST_ROOT=$(pwd)/test-tmp
       export NIX_BUILD_HOOK=
@@ -50,5 +53,12 @@ pkgs.runCommand "nixpkgs-lib-tests" {
       echo "Running lib/tests/sources.sh"
       TEST_LIB=$PWD/lib bash lib/tests/sources.sh
 
-    touch $out
-''
+      mkdir $out
+      echo success > $out/${nix.version}
+    '';
+
+in
+  pkgs.symlinkJoin {
+    name = "nixpkgs-lib-tests";
+    paths = map testWithNix nixVersions;
+  }