fix(api): don't call process.exit manually

[sheremet-va]

Description

fixes #5913

Vitest API will now throw an error (TestsNotFoundError) when calling start manually. Vitest will also throw GitNotFoundError error if changed flag was used but there is no git repository available.

Both of these errors can be imported from vitest/node.

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[sheremet-va]

Should also remove here:

vitest/test/test-utils/index.ts

Line 19 in 67d6add

process.exit = (() => { }) as never

[AriPerkkio]

This fixes #5913