fix: Fail expectations that throw non-Errors

[AaronMoat]

I hit a very strange error in one of my codebases (private, unfortunately, else I'd link to it). Here's a pretend example:

.expect((res) => {
  Buffer.from(undefined);
});

In normal environments, Buffer.from(undefined) throws a TypeError, which then correctly passes all instanceof Error checks. For reasons which I haven't fully diagnosed, but appear related to something to do with my setup (Jest? JSDom? Unsure.) and this warning, the below actually logs false:

.expect((res) => {
  try {
    Buffer.from(undefined);
  } catch (error) {
    console.log(error instanceof Error);
  }
});

Now, this is a silly example, but in my test I was trying to convert a buffer to a string and assert its string result. Something like:

.expect((res) =>
  expect(Buffer.from(res.body).toString('utf-8')).toBe(
    'some value',
  ),
);

For my example, what I actually wanted was res.body.toString (the Buffer.from was unnecessary), but it was throwing, and silently failing because of the above-described problem.

I tried a couple things, like trying to see if something "looks like" an error, but the simplest thing I could land on was to just simply covert non-errors to errors, and then the rest of the codebase is happy. Incidentally, and I would argue this is a good thing, it also now fails if you do throw 123, which while not a great throw, should probably fail, and previously did not.

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