nodejs: disable JS test suite on Darwin

This was recently enabled in NixOS#313982. It seems to be much too flaky
on Darwin currently, especially x86; see:

* <https://hydra.nixos.org/build/264860513/nixlog/8>
* <https://hydra.nixos.org/build/264956149/nixlog/3>
* <https://hydra.nixos.org/build/265094929/nixlog/3>
* <https://hydra.nixos.org/build/264901296/nixlog/3>

Disable these tests on macOS for now as the broken Node.js package
is holding up a lot of builds.

Fixes: b26563a

pkgs/development/web/nodejs/nodejs.nix

@@ -133,13 +133,15 @@ let
     # Some dependencies required for tools/doc/node_modules (and therefore
     # test-addons, jstest and others) target are not included in the tarball.
     # Run test targets that do not require network access.
-    checkTarget = lib.concatStringsSep " " [
+    checkTarget = lib.concatStringsSep " " ([
       "build-js-native-api-tests"
       "build-node-api-tests"
       "tooltest"
       "cctest"
+    ] ++ lib.optionals (!stdenv.isDarwin) [
+      # TODO: JS test suite is too flaky on Darwin; revisit at a later date.
       "test-ci-js"
-    ];
+    ]);
 
     checkFlags = [
       # Do not create __pycache__ when running tests.