docs: document config executing multiple times

[agg23]

Begins to address #34559. The config file will execute multiple times; at least once for the CLI process, then once for each worker. This can produce obscure issues depending on what the user is doing.

[github-actions]

Test results for "tests 1"

13 flaky

⚠️ [firefox-page] › tests/page/page-evaluate.spec.ts:403:3 › should throw for too deep reference chain @firefox-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/browsercontext-clearcookies.spec.ts:72:3 › should remove cookies by name regex @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/browsercontext-har.spec.ts:327:3 › should record overridden requests to har @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/browsercontext-viewport-mobile.spec.ts:157:5 › mobile viewport › mouse should work with mobile viewports and cross process navigations @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/browsercontext-viewport-mobile.spec.ts:206:5 › mobile viewport › view scale should reset after navigation @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/defaultbrowsercontext-2.spec.ts:28:3 › should work in persistent context @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/proxy.spec.ts:93:11 › should proxy local network requests › by default › loopback address @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/screenshot.spec.ts:278:14 › element screenshot › should restore viewport after page screenshot and exception @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/screenshot.spec.ts:291:14 › element screenshot › should restore viewport after page screenshot and timeout @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/video.spec.ts:475:5 › screencast › should scale frames down to the requested size @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-leaks.spec.ts:82:5 › click should not leak @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-leaks.spec.ts:161:5 › waitFor should not leak @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-screenshot.spec.ts:868:5 › page screenshot animations › should wait for fonts to load @webkit-ubuntu-22.04-node18

37730 passed, 654 skipped
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Merge workflow run.