chore(deps): update dependency @web/test-runner to v0.20.2 #4478

Job	Run time
Verify changes (lit-element)	17s
Verify changes (preact-htm)	17s
Verify changes (preact-jsx)	17s
Verify changes (preact-tsx)	17s
Verify changes (lit-element-ts-esbuild)	17s
Verify changes (html-test)	17s
Verify changes (guides/test-runner/playwright)	15s
Verify changes (visual-regression)	15s
Verify changes (guides/test-runner/responsive)	17s
Verify changes (react-jsx)	15s
Verify changes (snowpack-react)	14s
Verify changes (react-htm)	15s
Verify changes (guides/test-runner/getting-started)	14s
Verify changes (saucelabs)	16s
Verify changes (snowpack-lit)	17s
Verify changes (lit-element-ts-tsc)	17s
Verify changes (react-tsx)	13s
Verify changes (mock-es-module)	15s
Verify changes (playwright)	17s
Verify changes (import-maps)	17s
Verify changes (guides/test-runner/watch-and-debug)	5s
Verify changes (guides/test-runner/typescript)	17s
Verify changes (snowpack-svelte)	17s
Verify changes (puppeteer)	17s
	6m 15s

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