ci: fail php-qa jobs after 20 minutes instead of riding out a bad runner

[erikfrerejean]

Why

In run 31094035518 (PR #421), the PHP QA (fluent / PHP 8.3) job took 32 minutes while its 8.4/8.5 siblings finished in ~11.5 min and the base-matrix jobs in ~9 min. Investigation showed nothing wrong with the code or workflow:

• All three fluent jobs run the identical PHPUnit command and all used PCOV 1.0.12 as coverage driver.
• The overrun sat entirely inside the test step, smeared evenly across the DB-heavy suites (~3–5s/test vs the usual ~1–2s/test) — the signature of a degraded/contended hosted runner, not a hung test.
• The two earlier runs of the same PR ran fluent/8.3 in 11–12 minutes.

The slow job also held its runner slot, queueing E2E (chromium / tailwind) until it finished and stretching the run to ~39 minutes wall clock.

What

Add timeout-minutes: 20 to the php-qa job — roughly double the healthy fluent duration. A degenerate runner now fails fast instead of burning 3× the minutes; a re-run lands on a fresh runner.