fix(mocker)!: don't restore mock to the original if module is mocked

examples/mocks/test/automocking.spec.ts

@@ -56,8 +56,8 @@ test('automock properly restores mock', async () => {
     log.warn()
   }).not.toThrow()
 
-  expect(moduleWithSymbol[methodSymbol]()).toBe('hello')
-  expect(moduleWithSymbol.warn()).toBe('hello')
+  expect(moduleWithSymbol[methodSymbol]()).toBe(undefined)
+  expect(moduleWithSymbol.warn()).toBe(undefined)
 
   expect(log.warn).toHaveProperty('mockImplementation')
 })

packages/vitest/src/runtime/mocker.ts

@@ -278,7 +278,7 @@ export class VitestMocker {
           const mock = spyOn(newContainer, property).mockImplementation(() => undefined)
           mock.mockRestore = () => {
             mock.mockReset()
-            mock.mockImplementation(undefined!)
+            mock.mockImplementation(() => undefined)
             return mock
           }
           // tinyspy retains length, but jest doesn't.

test/core/test/mocked-no-mocks.test.ts

@@ -15,6 +15,7 @@ test('mocking several modules work', () => {
 
   mockedB()
 
-  expect(mockedA).toHaveBeenCalledTimes(2)
+  // mockedA is not called because mockedB is restored to be undefined
+  expect(mockedA).toHaveBeenCalledTimes(1)
   expect(mockedB).toHaveBeenCalledTimes(1)
 })