Fix CI runner-context validation

[PrzemyslawKlys]

Summary

• define the test-budget multiplier as matrix data available during job evaluation
• retain the existing 4x Linux budget and 1x macOS/Windows budgets

The current job-level runner.os expression is evaluated before a runner exists, so GitHub rejects the workflow without creating a job.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.01%. Comparing base (641cead) to head (f251e54).
⚠️ Report is 32 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #212      +/-   ##
==========================================
- Coverage   65.05%   65.01%   -0.04%     
==========================================
  Files         555      555              
  Lines       65191    65191              
  Branches    18449    18449              
==========================================
- Hits        42409    42383      -26     
- Misses      15398    15418      +20     
- Partials     7384     7390       +6     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.