fix(expect): Correct generic MatchersObject this type in expect.extend

[pengooseDev]

Description

fixes #6967

This PR fixes a TypeScript error where generic functions passed to expect.extend receive an incorrect this type. The issue was caused by the missing & ThisType<T> in the MatchersObject type definition.
I try to add a regression test, but I couldn't find an appropriate test example, so I've attached an image below.

Current

Fixed

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[hi-ogawa]

I try to add a regression test, but I couldn't find an appropriate test example

Thanks for the fix! Can we just add the repro here?

vitest/test/core/test/jest-expect.test.ts

Lines 206 to 207 in 1bf0f75

	it('expect.extend', async () => {
	expect.extend({

[pengooseDev]

@hi-ogawa
I just followed the team's convention with the new custom matcher test method toBeTestedMatcherContext.
If any additional changes are needed, please feel free to let me know.