chore(deps): update dependency @web/test-runner to v0.20.2 #4281

Job	Run time
Verify changes (lit-element)	41s
Verify changes (lit-element-ts-esbuild)	45s
Verify changes (lit-element-ts-tsc)	37s
Verify changes (html-test)	41s
Verify changes (preact-htm)	38s
Verify changes (preact-jsx)	43s
Verify changes (preact-tsx)	43s
Verify changes (puppeteer)	36s
Verify changes (playwright)	51s
Verify changes (import-maps)	42s
Verify changes (mock-es-module)	39s
Verify changes (visual-regression)	1s
Verify changes (saucelabs)	42s
Verify changes (guides/test-runner/getting-started)	37s
Verify changes (guides/test-runner/watch-and-debug)	36s
Verify changes (guides/test-runner/playwright)	48s
Verify changes (guides/test-runner/responsive)	37s
Verify changes (guides/test-runner/typescript)	42s
Verify changes (react-htm)	39s
Verify changes (react-jsx)	39s
Verify changes (react-tsx)	43s
Verify changes (snowpack-lit)	1s
Verify changes (snowpack-react)	1s
Verify changes (snowpack-svelte)	1s
	13m 43s

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