ci: package installs time out on their own

[mishan]

A slow or stalled package mirror used the jobs' time.

• Twice this week CI runs sat in apt-get install for one to two hours, against GitHub's six-hour default.
• On nettest: a room played over a bad network, measured #391, a slow mirror spent 13 minutes of the jam job's 30. jamtest was then cut off at the job limit with every check so far passing.

Changes

• Every step that installs from a package mirror gets timeout-minutes: 10. That covers apt-get, the wasm-trees action (which runs apt itself) and Playwright's --with-deps install. A stalled mirror now fails that step, and says so.
• The jam job's Playwright install becomes its own step, as the browser job's already is, so the limit applies to the install and not to jamtest.
• The three wasm test jobs go from 30 to 45 minutes. Their tests take about a quarter hour, which leaves room for a slow mirror without returning to hours.