gh-36670: .github/workflows/docker.yml: Interrupt the build before the 6 hour cancellation
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When a CI Linux workflow is canceled, because we are using `docker
build`, no image is written out.
Here we add an input parameter `timeout`, defaulting to 5.5 hours, after
which we kill the `make` process inside of the build container.
Then our script (in tox) writes out and pushes an image (marked as
"-failed") to ghcr.io, enabling better diagnostics.
See
https://github.com/mkoeppe/sage/actions/runs/6831246509/job/18580446041
for a test run where for demonstration purposes I set the timeout to 6
minutes.
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URL: https://github.com/sagemath/sage/pull/36670
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee
