[ct] task-queue-sk_test.js: Fix assertion.

This fixes the following error:

  Error: Invalid Chai property: class. Did you mean "has"?

Somehow the "expect(...).to.have.class('foo')" syntax stopped working after moving to the TypeScript-enabled Webpack configuration. Probably some kind of issue with the npm dependencies.

Two possible fixes:

1. Rewrite test to make an assertion directly against the element's className property.
2. Explicitly add support for the "to.have.class" syntax via chai-dom[1] and karma-chai-dom[2].

I chose to go with option 1 because it's the simplest and because AFAIK there's no other test in the repo that uses this syntax, but we can always switch to option 2 if anyone is interested.

[1] https://github.com/nathanboktae/chai-dom.
[2] https://github.com/nathanboktae/karma-chai-dom.

Bug: skia:10292
Change-Id: I8fcfaa9c2d3373558b3f97b2848f0950794f17eb
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/292735
Reviewed-by: Weston Tracey <westont@google.com>
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
diff --git a/ct/modules/task-queue-sk/task-queue-sk_test.js b/ct/modules/task-queue-sk/task-queue-sk_test.js
index ece9016..02c5a8e 100644
--- a/ct/modules/task-queue-sk/task-queue-sk_test.js
+++ b/ct/modules/task-queue-sk/task-queue-sk_test.js
@@ -75,9 +75,9 @@
   it('task details works', async () => {
     const table = await loadTableWithReplies([resultSetOneItem]);
 
-    expect($$('.dialog-background', table)).to.have.class('hidden');
+    expect($$('.dialog-background', table).className).to.contain('hidden');
     $$('.details', table).click();
 
-    expect($$('.dialog-background', table)).to.not.have.class('hidden');
+    expect($$('.dialog-background', table).className).to.not.contain('hidden');
   });
 });