Unclear solution to throwError deprecation

[Martinspire]

So for Angular httpClient I have used a few catchError items to handle various problems with the data from my API.
With my unit tests I have used throwError to test my logic.

But recently I've started to see deprecation messages around throwError and I can't figure out what syntax I'm supposed to use now because its not clear what the error is referring to.

    const mockError = new HttpErrorResponse({ status: 404, statusText: 'Not Found' });
    mockHttpClient.get.mockImplementation(() => throwError(() => mockError));

In this block of code the message in VSCode is as follows:

Deprecated: The scheduler parameter will be removed in v8.
Use throwError in combination with {@link observeOn}: throwError(() => new Error('test')).pipe(observeOn(scheduler));.
Details: https://rxjs.dev/deprecations/scheduler-argument

I'm using eslint to spot these deprecations, but I don't really get why I suddenly need a pipe and what the heck to put in the observer. The scheduler parameter will be removed message is throwing me off because I'm not adding a scheduler. I'm just adding my mock as a return since that was already needed for the previous deprecation of throwError (which was also a bit unclear in the messaging, but I got it going).