task: upgrade jest and nock to support native fetch

[toufali]

Because

Tests fail when using native Fetch API, blocking our migration away from Axios

This pull request

Upgrades Jest and Nock to versions that are known to support the native Fetch API

Issue that this pull request solves

Closes: FXA-11503

Checklist

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• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).

[toufali]

Closing this in favor of #18698 .

Nock was not built for native fetch. A recent release suggests it can work, but after upgrading and going down that path I found too many work-arounds were needed, including importing text-encoder/decoder for all nock test files, and installing yet another dependency, @mswjs/interceptors. Since one of the original goals was to remove dependencies, I decided on a different approach, replacing nock with fetch-mock (which is already used/installed in our codebase).

Since fetch-mock doesn't work with Axios (and vice-versa) I'll complete this replacement together with native fetch in #18698