h2o.tests: fix the eval

Without the change `h2o.tests` eval fails as:

    $ nix build --no-link -f. h2o.tests
    error:
       … while evaluating the attribute 'h2o'
         at pkgs/by-name/h2/h2o/package.nix:78:36:
           77|   passthru = {
           78|     tests = { inherit (nixosTests) h2o; };
             |                                    ^
           79|   };

       … in the left operand of the update (//) operator
         at pkgs/top-level/all-packages.nix:153:5:
          152|   nixosTests =
          153|     import ../../nixos/tests/all-tests.nix {
             |     ^
          154|       inherit pkgs;

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: undefined variable 'lib'
       at nixos/tests/all-tests.nix:676:44:
          675|   gvisor = runTest ./gvisor.nix;
          676|   h2o = import ./web-servers/h2o { inherit lib runTest; };
             |                                            ^
          677|   hadoop = import ./hadoop {

nixos/tests/all-tests.nix

@@ -673,7 +673,10 @@ in
   guacamole-server = runTest ./guacamole-server.nix;
   guix = handleTest ./guix { };
   gvisor = runTest ./gvisor.nix;
-  h2o = import ./web-servers/h2o { inherit runTest; };
+  h2o = import ./web-servers/h2o {
+    inherit runTest;
+    inherit (pkgs) lib;
+  };
   hadoop = import ./hadoop {
     inherit handleTestOn;
     package = pkgs.hadoop;