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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### 📝 Checklist

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- [ ] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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- Depends on #36616 (merged here)

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URL: #36627
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee

.github/workflows/ci-linux.yml

@@ -34,39 +34,20 @@ permissions:
 
 jobs:
 
-  # standard-pre for the default platform (used by build.yml etc.)
-  default-pre:
+  # standard-pre and standard (without ptest) for the default platform (used by build.yml etc.)
+  default:
     uses: ./.github/workflows/docker.yml
     with:
       # Build from scratch
-      docker_targets: "with-system-packages configured with-targets-pre"
+      docker_targets: "with-system-packages configured with-targets-pre with-targets"
       # FIXME: duplicated from env.TARGETS
       targets_pre: all-sage-local
-      tox_system_factors: >-
-        ["ubuntu-focal"]
-      tox_packages_factors: >-
-        ["standard"]
-      docker_push_repository: ghcr.io/${{ github.repository }}/
-
-  # standard for the default platform (used by build.yml etc.)
-  default:
-    if: ${{ success() || failure() }}
-    needs: [default-pre]
-    uses: ./.github/workflows/docker.yml
-    with:
-      # Build incrementally from previous stage (pre)
-      incremental: true
-      free_disk_space: true
-      from_docker_repository: ghcr.io/${{ github.repository }}/
-      from_docker_target: "with-targets-pre"
-      docker_targets: "with-targets with-targets-optional"
-      # FIXME: duplicated from env.TARGETS
       targets: build doc-html
       targets_optional: ptest
       tox_system_factors: >-
         ["ubuntu-focal"]
       tox_packages_factors: >-
-          ["standard"]
+        ["standard"]
       docker_push_repository: ghcr.io/${{ github.repository }}/
 
   # All platforms. This duplicates the default platform, but why not,
@@ -158,8 +139,6 @@ jobs:
 
   minimal-pre:
     if: ${{ success() || failure() }}
-    # It does not really "need" it.
-    needs: [standard]
     uses: ./.github/workflows/docker.yml
     with:
       # Build from scratch
@@ -169,8 +148,9 @@ jobs:
       tox_packages_factors: >-
           ["minimal"]
       docker_push_repository: ghcr.io/${{ github.repository }}/
-      # Reduce from 30 to 25 because it may run in parallel with 'standard-sitepackages' above
-      max_parallel: 25
+      # Reduced from 30 because it may run in parallel with 'standard-sitepackages' above.
+      # Calibrated for clogging the job pipeline until the "default" job has finished.
+      max_parallel: 20
 
   minimal:
     if: ${{ success() || failure() }}