PR builds killed during Ubuntu test compile

[itowlson]

Ongoing problem, see eg https://github.com/spinframework/spin/actions/runs/18451759414/job/52566336947?pr=3290

It's happening often enough to be slowing us down but we can usually get thigs through with 2-4 re-runs.

[itowlson]

Looking healthier post #3304. Bumping down to non-critical and possibly fixed - revisit in a week or so.

[itowlson]

Appears fixed. Thank you @tschneidereit!