chore(deps): update dependency @open-wc/testing to v4 #4481

Job	Run time
Verify changes (html-test)	16s
Verify changes (lit-element-ts-tsc)	15s
Verify changes (preact-htm)	15s
Verify changes (puppeteer)	14s
Verify changes (preact-tsx)	17s
Verify changes (lit-element)	17s
Verify changes (preact-jsx)	17s
Verify changes (import-maps)	15s
Verify changes (visual-regression)	17s
Verify changes (lit-element-ts-esbuild)	15s
Verify changes (guides/test-runner/getting-started)	14s
Verify changes (guides/test-runner/watch-and-debug)	17s
Verify changes (playwright)	17s
Verify changes (mock-es-module)	17s
Verify changes (react-tsx)	18s
Verify changes (react-jsx)	16s
Verify changes (snowpack-svelte)	17s
Verify changes (react-htm)	18s
Verify changes (snowpack-lit)	18s
Verify changes (snowpack-react)	18s
Verify changes (guides/test-runner/typescript)	16s
Verify changes (saucelabs)	15s
Verify changes (guides/test-runner/responsive)	15s
Verify changes (guides/test-runner/playwright)	16s
	6m 30s

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