fix(ci): codecov-action input is files, not file

[skl]

Version 5 of the codecov-action changed the input argument file --> files:

• https://github.com/codecov/codecov-action/blob/main/README.md#migration-guide

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.41%. Comparing base (9cf7b44) to head (10277ba).
⚠️ Report is 48 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (9cf7b44) and HEAD (10277ba). Click for more details.

HEAD has 2 uploads less than BASE

Flag	BASE (9cf7b44)	HEAD (10277ba)
unittests	1	0
integration-test	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #538      +/-   ##
==========================================
- Coverage   69.64%   61.41%   -8.24%     
==========================================
  Files         222      189      -33     
  Lines       23118    20804    -2314     
==========================================
- Hits        16101    12776    -3325     
- Misses       6184     7137     +953     
- Partials      833      891      +58     

Flag	Coverage Δ
integration-test	?
integration-test-arm	34.41% <ø> (?)
k8s-integration-test	51.41% <ø> (+0.30%)	⬆️
oats-test	35.86% <ø> (+0.04%)	⬆️
unittests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 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.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.