fix: remove codecov after_n_builds so single-submodule PRs report coverage (#6056)

`after_n_builds: 4` made Codecov wait for four coverage uploads before
finalizing a report. But this repo's CI runs unit tests only for the
submodules a PR changes (detect-changes), so a PR touching 1-3 submodules
produces fewer than four uploads. Codecov then waits forever and never
posts a report or status.

Observed on PR #6055 (changed only sagemaker-mlops): the mlops unit-test
job uploaded coverage successfully, but Codecov reported state=error,
sessions=0 and posted no codecov/project or codecov/patch status, because
it was still waiting for three more uploads that never come.

Drop the fixed count and rely on `wait_for_ci: true`, which finalizes the
report once CI completes using whatever uploaded — correct for this repo's
dynamic per-submodule CI.

Author: jam-jee

codecov.yml

@@ -12,10 +12,14 @@
 # The `ignore:` list below scopes the Codecov report to product code only.
 
 codecov:
-  # Wait for all four sub-package unit-test jobs to upload before finalizing, so the
-  # project % is computed over the complete report rather than whichever job lands first.
+  # Finalize the report only after CI completes. Do NOT pin a fixed upload count:
+  # this repo's CI runs unit tests per CHANGED submodule (detect-changes), so a PR
+  # touching only 1-3 submodules produces fewer than 4 uploads. A fixed
+  # `after_n_builds: 4` would make Codecov wait forever on those PRs and never post a
+  # report (observed on PR #6055, which changed only sagemaker-mlops: state=error,
+  # sessions=0, no status). `wait_for_ci: true` alone waits for CI and finalizes
+  # whatever uploaded, regardless of submodule count.
   notify:
-    after_n_builds: 4
     wait_for_ci: true
 
 coverage: