Fix source status sorting in admin

[codecov[bot]]

Codecov Report

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

Comparison is base (1573f61) 94.96% compared to head (ee6edb5) 94.98%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #552 +/- ## ========================================== + Coverage 94.96% 94.98% +0.01% ========================================== Files 81 81 Lines 2959 2970 +11 ========================================== + Hits 2810 2821 +11 Misses 149 149 ``` | [Flag](https://app.codecov.io/gh/Terralego/TerraVisu/pull/552/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Terralego) | Coverage Δ | | |---|---|---| | [backend-unittests](https://app.codecov.io/gh/Terralego/TerraVisu/pull/552/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Terralego) | `94.98% <100.00%> (+0.01%)` | :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=Terralego#carryforward-flags-in-the-pull-request-comment) to find out more.

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