ci: Reduce build job count to 2

[paulgessinger]

We've been getting OOM errors in the build again. This works around that.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7118769) 48.85% compared to head (a56f9d4) 48.85%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2954   +/-   ##
=======================================
  Coverage   48.85%   48.85%           
=======================================
  Files         495      495           
  Lines       28906    28906           
  Branches    13731    13731           
=======================================
  Hits        14121    14121           
  Misses       4899     4899           
  Partials     9886     9886           

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[github-actions]

📊: Physics performance monitoring for a56f9d4

Full contents

physmon summary

• ✅ CKF truth_smeared
• ✅ IVF truth_smeared
• ✅ AMVF truth_smeared
• ✅ Track Summary CKF truth_smeared
• ✅ Seeding truth_estimated
• ✅ CKF truth_estimated
• ✅ IVF truth_estimated
• ✅ AMVF truth_estimated
• ✅ Track Summary CKF truth_estimated
• ✅ Seeding seeded
• ✅ CKF seeded
• ✅ IVF seeded
• ✅ AMVF seeded
• ✅ AMVF (+grid seeder) seeded
• ✅ Track Summary CKF seeded
• ✅ Seeding orthogonal
• ✅ CKF orthogonal
• ✅ IVF orthogonal
• ✅ AMVF orthogonal
• ✅ Track Summary CKF orthogonal
• ✅ Ambisolver seeded
• ✅ Ambisolver orthogonal
• ✅ Seeding ttbar
• ✅ CKF ttbar
• ✅ Ambisolver
• ✅ Track Summary CKF ttbar
• ✅ AMVF ttbar
• ✅ AMVF (+grid seeder) ttbar
• ✅ Truth tracking (GSF)
• ✅ Truth tracking
• ✅ Particles fatras
• ✅ Particles geant4

[acts-project-service]

✅ Athena integration test results

✅ All tests successful

status	job	report
🟢	run_unit_tests
🟢	test_ActsEFTrackFit
🟢	test_ActsBenchmarkWithSpot
🟢	test_ActsConversionWorkflow
🟢	test_ActsWorkflow
🟢	test_ActsValidateAmbiguityResolution
🟢	test_ActsValidateResolvedTracks
🟢	test_ActsValidateTracks
🟢	test_ActsValidateActsCoreSpacePoints
🟢	test_ActsValidateActsSpacePoints
🟢	test_ActsValidateSeeds
🟢	test_ActsValidateOrthogonalSeeds
🟢	test_ActsValidateClusters
🟢	test_ActsPersistifyEDM
🟢	test_ActsGSFRefitting
🟢	test_ActsKfRefitting
🟢	test_ActsExtrapolationAlgTest
🟢	test_ActsITkTest
🟢	run_workflow_tests_run4_mc
🟢	run_workflow_tests_run2_mc
🟢	run_workflow_tests_run2_data
🟢	run_workflow_tests_run3_mc
🟢	run_workflow_tests_run3_data
🟢	run_art_test: test_data18_13TeV_1000evt
🟢	run_art_test: test_ttbarPU40_reco