docs: improve toHaveClass paramter description

[yury-s]

Fixes #34343

[github-actions]

Test results for "tests 1"

10 flaky

⚠️ [firefox-page] › tests/page/page-evaluate.spec.ts:403:3 › should throw for too deep reference chain @firefox-ubuntu-22.04-node18
⚠️ [firefox-page] › tests/page/workers.spec.ts:106:3 › should clear upon navigation @firefox-ubuntu-22.04-node18
⚠️ [chromium-library] › tests/library/popup.spec.ts:264:3 › should not throw when click closes popup @ubuntu-20.04-chromium-tip-of-tree
⚠️ [chromium-library] › tests/library/trace-viewer.spec.ts:1103:1 › should update highlight when typing locator @ubuntu-20.04-chromium-tip-of-tree
⚠️ [webkit-library] › tests/library/inspector/cli-codegen-1.spec.ts:200:7 › cli codegen › should work with TrustedTypes @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/trace-viewer.spec.ts:109:1 › should show tracing.group in the action list with location @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/trace-viewer.spec.ts:1243:1 › should pick locator in iframe @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/trace-viewer.spec.ts:1575:1 › canvas clipping in iframe @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-set-input-files.spec.ts:147:3 › should upload large file @webkit-ubuntu-22.04-node18
⚠️ [playwright-test] › tests/ui-mode-test-watch.spec.ts:145:5 › should watch all @windows-latest-node18-1

37588 passed, 648 skipped
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