[INF] Merge codecov.yml into tests.yml

[Zeroto521]

PR Description

Please describe the changes proposed in the pull request:

Fix code coverage difference in the dev branch, PR, and envs.
Get the same coverage result from the dev branch and PR.

The way of launching pytest is thiny different. And that causes the code coverage sometimes passed sometimes failed.

pyjanitor/.github/workflows/tests.yml

Line 42 in 8445dc0

pytest -m "${{ matrix.test-subset }}"

pyjanitor/.github/workflows/codecov.yml

Line 37 in 8445dc0

pytest

PR Checklist

Please ensure that you have done the following:

1. PR in from a fork off your branch. Do not PR from <your_username>:dev, but rather from <your_username>:<feature-branch_name>.

2. If you're not on the contributors list, add yourself to AUTHORS.md.

3. Add a line to CHANGELOG.md under the latest version header (i.e. the one that is "on deck") describing the contribution.
   • Do use some discretion here; if there are multiple PRs that are related, keep them in a single line.

Automatic checks

There will be automatic checks run on the PR. These include:

• Building a preview of the docs on Netlify
• Automatically linting the code
• Making sure the code is documented
• Making sure that all tests are passed
• Making sure that code coverage doesn't go down.

Relevant Reviewers

Please tag maintainers to review.

• @ericmjl

[Zeroto521]

Another reason code coverage failed is that pytest doesn't add --cov-append option.
--cov-append can get a sum coverage. I'll add this option in the next PR.
First let us merge codecov.yml into tests.yml. Keep the same test logic for the dev branch or a PR.

[codecov]

Codecov Report

Merging #1185 (0e9804a) into dev (8445dc0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1185   +/-   ##
=======================================
  Coverage   97.70%   97.70%           
=======================================
  Files          76       76           
  Lines        3482     3482           
=======================================
  Hits         3402     3402           
  Misses         80       80           

[Zeroto521]

That failed due to we pushed coverage separately.
So that's the latest coverage.

Add --cov-append for pytest can get a sum coverage.

[ericmjl]

Ah, that is now making sense! Thank you for figuring this out, @Zeroto521!