deepEqual returns true for different promise instances

[mantoni]

• library version : 5.3.1 (current)
• Environment : node 14

What did you expect to happen?

samsam.deepEqual returns false for different promise objects.

What actually happens

samsam.deepEqual returns true for different promise objects.

How to reproduce

const samsam = require('@sinonjs/samsam');

const p1 = Promise.resolve('a');
const p2 = Promise.resolve('b');
console.log(samsam.deepEqual(p1, p2)); // should return false

Reported in Sinon: sinonjs/sinon#2345

[fatso83]

verified fixed by #217