Updating codecov to v4

[raivisdejus]

Updating codecov action to v4 as the v3 uses node 16 and is deprecated.

codecov/codecov-action@v4 no longer supports tokenless uploading.

@chidiwilliams To support v4 the CODECOV_TOKEN should be added to repo secrets

[chidiwilliams]

Updated the secret. Will merge and test. Thanks.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.49%. Comparing base (ddebccc) to head (5658b16).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #770 +/- ## ========================================== + Coverage 82.39% 82.49% +0.10% ========================================== Files 83 83 Lines 3948 3948 ========================================== + Hits 3253 3257 +4 + Misses 695 691 -4 ``` | [Flag](https://app.codecov.io/gh/chidiwilliams/buzz/pull/770/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | Coverage Δ | | |---|---|---| | [Linux](https://app.codecov.io/gh/chidiwilliams/buzz/pull/770/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `80.54% <ø> (-0.06%)` | :arrow_down: | | [Windows](https://app.codecov.io/gh/chidiwilliams/buzz/pull/770/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `?` | | | [macOS](https://app.codecov.io/gh/chidiwilliams/buzz/pull/770/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams) | `82.06% <ø> (+0.10%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Chidi+Williams#carryforward-flags-in-the-pull-request-comment) to find out more.

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