ci: Update codecov-action to v2 API

[matthewfeickert]

Description

Requires PR #1622 to go in first.

Update codecov/codecov-action to v2 API as v1 API is being deprecated in 2022.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Update to codecov/codecov-action v2
   - c.f. https://github.com/codecov/codecov-action
   - Update `file` -> `files`

[codecov]

Codecov Report

Merging #1623 (e5f6728) into master (7ecaa63) will not change coverage.
The diff coverage is n/a.

❗ Current head e5f6728 differs from pull request most recent head cfd3e13. Consider uploading reports for the commit cfd3e13 to get more accurate results

@@           Coverage Diff           @@
##           master    #1623   +/-   ##
=======================================
  Coverage   97.70%   97.70%           
=======================================
  Files          63       63           
  Lines        4048     4048           
  Branches      576      576           
=======================================
  Hits         3955     3955           
  Misses         54       54           
  Partials       39       39           

Flag	Coverage Δ
contrib	25.44% <ø> (ø)
unittests	97.48% <ø> (ø)

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

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bc4b24a...cfd3e13. Read the comment docs.

[matthewfeickert]

Semantic PRs is currently down zeke/semantic-pull-requests#162, so can ignore the fact that the check is still "Expected"