Flaky test: Playwright e2e authentication › login happy path

[praseodym]

The 'authentication › login happy path' test (e2e-tests\authentication.e2e.ts:10:3) failed multiple times, but not always, in Firefox on Windows:

• https://github.com/kiesraad/abacus/actions/runs/13205374900/job/36867557887
• https://github.com/kiesraad/abacus/actions/runs/13200732829/job/36852158206
• https://github.com/kiesraad/abacus/actions/runs/13181694700/job/36794180864
• https://github.com/kiesraad/abacus/actions/runs/13210768955/job/36883785814
• https://github.com/kiesraad/abacus/actions/runs/13236735808/job/36943341433
• https://github.com/kiesraad/abacus/actions/runs/13237238693/job/36944958762

It's tricky to debug this, maybe uploading the Playwright report as an artifact would help here.

For the Playwright report, we need --reporter=html. And we need to decide/check which folder it gets written to, so we can upload the correct folder. Output dir can be set with PLAYWRIGHT_HTML_OUTPUT_DIR or through the config file.

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PR to enable Playwright reports in pipeline: #1010