chore(deps): update dependency @web/test-runner to v0.20.2 #4367

Job	Run time
Verify changes (lit-element-ts-esbuild)	19s
Verify changes (lit-element-ts-tsc)	18s
Verify changes (preact-jsx)	20s
Verify changes (lit-element)	18s
Verify changes (playwright)	1s
Verify changes (html-test)	19s
Verify changes (puppeteer)	20s
Verify changes (preact-tsx)	1s
Verify changes (preact-htm)	18s
Verify changes (mock-es-module)	19s
Verify changes (visual-regression)	19s
Verify changes (guides/test-runner/playwright)	23s
Verify changes (saucelabs)	21s
Verify changes (import-maps)	19s
Verify changes (guides/test-runner/responsive)	21s
Verify changes (guides/test-runner/getting-started)	22s
Verify changes (guides/test-runner/watch-and-debug)	18s
Verify changes (react-jsx)	18s
Verify changes (react-htm)	21s
Verify changes (react-tsx)	20s
Verify changes (guides/test-runner/typescript)	21s
Verify changes (snowpack-svelte)	1s
Verify changes (snowpack-react)	19s
Verify changes (snowpack-lit)	24s
	7m 0s

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