Reinstate Codecov in CI

[akx]

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

Description of change

This PR:

• reinstates (and upgrades) the codecov CI action that was removed in Add support for new TDIGEST features and changes #2392 (321c57f).

[dvora-h]

Why not just uncomment lines 84-88?

[codecov-commenter]

Codecov Report

Base: 92.24% // Head: 92.11% // Decreases project coverage by -0.12% ⚠️

Coverage data is based on head (a40789f) compared to base (66c4e60).
Patch coverage: 99.35% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2394      +/-   ##
==========================================
- Coverage   92.24%   92.11%   -0.13%     
==========================================
  Files         111      110       -1     
  Lines       28814    28881      +67     
==========================================
+ Hits        26579    26605      +26     
- Misses       2235     2276      +41     

Impacted Files	Coverage Δ
redis/commands/bf/__init__.py	100.00% <ø> (ø)
redis/commands/bf/commands.py	98.00% <95.23%> (-0.42%)	⬇️
redis/commands/bf/info.py	100.00% <100.00%> (ø)
tests/test_asyncio/test_bloom.py	98.58% <100.00%> (-1.00%)	⬇️
tests/test_bloom.py	98.68% <100.00%> (-0.95%)	⬇️
redis/compat.py	50.00% <0.00%> (-50.00%)	⬇️
tests/test_asyncio/compat.py	75.00% <0.00%> (-25.00%)	⬇️
redis/__init__.py	85.71% <0.00%> (-4.77%)	⬇️
redis/retry.py	95.83% <0.00%> (-4.17%)	⬇️
redis/asyncio/retry.py	92.85% <0.00%> (-3.58%)	⬇️
... and 21 more

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[akx]

@dvora-h

Why not just uncomment lines 84-88?

Because the commented lines above it were/are on the wrong indent level, and it was hard to see the correct indentation without moving the block.

Also, the execution order of the "show results" action and this don't really matter.

This also changes the action version to v3, and removes the token line, so the diff is probably about the same size regardless.

[dvora-h]

The execution order really doesn't matter, but:

1. We prefer to include the name.
2. I don't understand why we don't need the token?

[akx]

The execution order really doesn't matter, but:

1. We prefer to include the name.

Well, sure, I can put it back. 🤷

2. I don't understand why we don't need the token?

Because this is a public/OSS repository, and public repositories don't need tokens on Codecov.