Update jest tests that have restored spyOn mocks

In the latest Jest, jest.restoreAllMocks() seems to restore also other
kind of mocks than jest.spyOn().

test/browser.ts

@@ -5,13 +5,13 @@ import { applyCustomElements } from '../src/custom-elements/browser'
 
 const polyfillCleanup = jest.fn()
 
-jest.mock('@marp-team/marpit-svg-polyfill', () => ({
-  observe: jest.fn(() => polyfillCleanup),
-}))
-
+jest.mock('@marp-team/marpit-svg-polyfill')
 jest.mock('../src/custom-elements/browser')
 
-beforeEach(() => jest.clearAllMocks())
+beforeEach(() => {
+  jest.clearAllMocks()
+  ;(observe as jest.Mock).mockReturnValue(polyfillCleanup)
+})
 afterEach(() => jest.restoreAllMocks())
 
 describe('Browser script', () => {

test/custom-elements/browser.ts

@@ -39,7 +39,6 @@ beforeAll(() => {
 })
 
 afterEach(() => {
-  jest.restoreAllMocks()
   window[browser.marpCustomElementsRegisteredSymbol] = false
 
   // Reset custom elements defined in JSDOM
@@ -100,6 +99,12 @@ describe('The hydration script for custom elements', () => {
           .mockReturnValue(false)
       })
 
+      afterEach(() => {
+        ;(
+          browser.isSupportedCustomizedBuiltInElements as jest.Mock
+        ).mockRestore()
+      })
+
       it('replaces all of elements that are using "is" attribute to the standalone custom element', () => {
         document.body.innerHTML = Object.keys(elements)
           .map((elm) => `<${elm} is="marp-${elm}"></${elm}>`)