CI: use new version of codecov action

[psafont]

Testing, it's not clear whether this works, or needs some kind of setup in the github side, or codecov side

Upload works, it's the coverage that keeps being wonky

[codecov[bot]]

Codecov Report

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

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5734 +/- ## ======================================== - Coverage 45.5% 44.8% -0.7% ======================================== Files 13 16 +3 Lines 1624 2210 +586 ======================================== + Hits 739 992 +253 - Misses 885 1218 +333 ``` [see 8 files with indirect coverage changes](https://app.codecov.io/gh/xapi-project/xen-api/pull/5734/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | [Flag](https://app.codecov.io/gh/xapi-project/xen-api/pull/5734/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | Coverage Δ | | |---|---|---| | [python2.7](https://app.codecov.io/gh/xapi-project/xen-api/pull/5734/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | `45.5% <ø> (ø)` | | | [python3.11](https://app.codecov.io/gh/xapi-project/xen-api/pull/5734/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | `51.4% <ø> (?)` | | 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=xapi-project#carryforward-flags-in-the-pull-request-comment) to find out more.

[psafont]

The mysteries of the ever-shifting coverage ...