chore(deps): update dependency @web/test-runner to v0.20.2 #4449

Job	Run time
Verify changes (preact-jsx)	19s
Verify changes (puppeteer)	18s
Verify changes (lit-element)	17s
Verify changes (lit-element-ts-tsc)	19s
Verify changes (mock-es-module)	19s
Verify changes (preact-htm)	19s
Verify changes (guides/test-runner/playwright)	20s
Verify changes (guides/test-runner/getting-started)	21s
Verify changes (visual-regression)	17s
Verify changes (lit-element-ts-esbuild)	17s
Verify changes (html-test)	20s
Verify changes (react-jsx)	22s
Verify changes (preact-tsx)	20s
Verify changes (guides/test-runner/responsive)	22s
Verify changes (import-maps)	20s
Verify changes (saucelabs)	6s
Verify changes (guides/test-runner/watch-and-debug)	19s
Verify changes (snowpack-lit)	19s
Verify changes (react-htm)	20s
Verify changes (guides/test-runner/typescript)	20s
Verify changes (react-tsx)	21s
Verify changes (playwright)	20s
Verify changes (snowpack-react)	17s
Verify changes (snowpack-svelte)	18s
	7m 30s

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