test: unflake selenium tests

[mxschmitt]

This gives every worker a range of 5 ports. The problem was that one test used another's port.

Fixes https://github.com/microsoft/playwright/actions/runs/14958189017/job/42016648248#step:6:2002.

[github-actions]

Test results for "tests 1"

7 flaky

⚠️ [firefox-library] › library/inspector/cli-codegen-1.spec.ts:986:7 › cli codegen › should not throw csp directive violation errors @firefox-ubuntu-22.04-node18
⚠️ [firefox-library] › library/inspector/cli-codegen-3.spec.ts:222:7 › cli codegen › should generate frame locators (4) @firefox-ubuntu-22.04-node18
⚠️ [webkit-library] › library/browsercontext-viewport-mobile.spec.ts:97:5 › mobile viewport › should fire orientationchange event @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › library/ignorehttpserrors.spec.ts:30:3 › should isolate contexts @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › library/screenshot.spec.ts:205:14 › element screenshot › element screenshot should work with a mobile viewport @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › page/page-screenshot.spec.ts:345:5 › page screenshot › should work while navigating @webkit-ubuntu-22.04-node18
⚠️ [playwright-test] › ui-mode-test-watch.spec.ts:145:5 › should watch all @windows-latest-node18-1

39165 passed, 803 skipped
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Merge workflow run.