Set comparison with eql is wrong

expect(new Set([1])).not.to.be.eql(new Set([2])); // fails

You get the following output:
Error: expected {} to sort of not equal {}
Expected :{}
Actual :{}

I can work on a PR for this.

Start by reproducing the Set comparison example from the issue and locate the equality-comparison entry point used by eql. Add a regression test covering Sets with different values; done means the example passes and the test verifies that the Sets are not considered equal.

Written by the indexing model from the issue text.