Wait for both coverage uploads before notifying

[philipcraig]

Codecov posts the project status after the first upload, so the runtime-only report is compared against a base that also carries the consteval flag and fails the 1% threshold (seen on #282). Set after_n_builds: 2 so the comparison waits for both uploads.

[jbcoe]

Thanks for this. The previous setup did confuse me a bit.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.87%. Comparing base (d9ca248) to head (66905c1).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #289   +/-   ##
=======================================
  Coverage   72.87%   72.87%           
=======================================
  Files           9        9           
  Lines         822      822           
  Branches      208      208           
=======================================
  Hits          599      599           
  Misses         24       24           
  Partials      199      199           

Flag	Coverage Δ
consteval	97.46% <ø> (ø)
runtime	70.25% <ø> (ø)

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