chore(deps): update dependency @open-wc/testing to v4 #4395

Job	Run time
Verify changes (html-test)	20s
Verify changes (lit-element-ts-tsc)	21s
Verify changes (lit-element-ts-esbuild)	18s
Verify changes (preact-jsx)	21s
Verify changes (lit-element)	21s
Verify changes (preact-tsx)	19s
Verify changes (preact-htm)	21s
Verify changes (mock-es-module)	20s
Verify changes (visual-regression)	19s
Verify changes (import-maps)	20s
Verify changes (playwright)	18s
Verify changes (guides/test-runner/responsive)	19s
Verify changes (guides/test-runner/playwright)	18s
Verify changes (guides/test-runner/typescript)	22s
Verify changes (puppeteer)	18s
Verify changes (guides/test-runner/getting-started)	20s
Verify changes (saucelabs)	9s
Verify changes (snowpack-lit)	22s
Verify changes (react-jsx)	18s
Verify changes (react-htm)	26s
Verify changes (snowpack-react)	8s
Verify changes (react-tsx)	28s
Verify changes (snowpack-svelte)	10s
Verify changes (guides/test-runner/watch-and-debug)	7s
	7m 23s

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