build(deps): replace `@gr2m/fetch-mock` with `fetch-mock`

[wolfy1339]

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Before the change?

• Used a custom fork of fetch-mock for Fetch API support

After the change?

• Use the fetch-mock module again, it has been updated to support the Fetch API

Pull request checklist

• [x] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• [ ] Yes
• [x] No

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[wolfy1339]

The tests are failing because of some type errors with fetch-mock, otherwise the tests are passing

[oscard0m]

The tests are failing because of some type errors with fetch-mock, otherwise the tests are passing

Are these type errors something we can fix on our end or it needs work in fetch-mock?

[wolfy1339]

Are these type errors something we can fix on our end or it needs work in fetch-mock?

These type errors are not because of our code. We could always override the types, but that's not a great way to do it over the 50 repositories that use fetch-mock.

See this PR https://github.com/wheresrhys/fetch-mock/pull/680

It's because the package offers CJS+ESM but the types only have a CJS export and this TypeScript complains that there is no default export defined.

The problem has been fixed, just waiting for the release to drop on npm

[wolfy1339]

This is now ready to merge