Ensure manager gets set into runner group creation

[codecov-commenter]

Codecov Report

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

Project coverage is 85.92%. Comparing base (3a88a76) to head (fddecca).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #588 +/- ## ======================================= Coverage 85.92% 85.92% ======================================= Files 31 31 Lines 1243 1243 ======================================= Hits 1068 1068 Misses 175 175 ``` | [Flag](https://app.codecov.io/gh/scality/runner-manager/pull/588/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scality) | Coverage Δ | | |---|---|---| | [api](https://app.codecov.io/gh/scality/runner-manager/pull/588/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scality) | `66.53% <50.00%> (ø)` | | | [unit](https://app.codecov.io/gh/scality/runner-manager/pull/588/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scality) | `71.19% <100.00%> (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=scality#carryforward-flags-in-the-pull-request-comment) to find out more.

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