gh-36627: CI Linux: Build the default platform in one job
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This job is the combination of the "default-pre" job and the first half
of the "default" job (with `make ptest` removed). It takes about 4 hours
and so it fits robustly in the 6h job limit. (Test run:
https://github.com/mkoeppe/sage/actions/runs/6727624213/job/18285698639)
Together with #36616, which deliberately clogs the pipeline with ~50
"standard-pre" jobs, this gives the following behavior when a release
tag is pushed:
- "default" is scheduled
- ~45 "standard-pre" jobs are scheduled (runtime 0.5 to 4 hours)
- ~45 "minimal-pre" jobs (with max-parallel = 20) are scheduled (3 to 4
hours)
- this is calibrated (and can be recalibrated later) so as to keep CI
jobs from PRs waiting until the Docker image built by "default" is
available.
During the clogging time, developers can rebase their PRs to the latest
develop.
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### :hourglass: Dependencies
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- Depends on #36616 (merged here)
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URL: https://github.com/sagemath/sage/pull/36627
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee
