:white_check_mark: Add delete namespace ut back

[codecov[bot]]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (9deb3f0) 34.84% compared to head (5e985ff) 35.05%.

Files	Patch %	Lines
pkg/handlers/namespaces/namespaces_delete.go	60.00%	3 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #284 +/- ## ========================================== + Coverage 34.84% 35.05% +0.20% ========================================== Files 132 131 -1 Lines 9260 9100 -160 ========================================== - Hits 3227 3190 -37 + Misses 5706 5590 -116 + Partials 327 320 -7 ``` | [Flag](https://app.codecov.io/gh/go-sigma/sigma/pull/284/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-sigma) | Coverage Δ | | |---|---|---| | [unit-test-mysql](https://app.codecov.io/gh/go-sigma/sigma/pull/284/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-sigma) | `35.05% <71.42%> (+0.20%)` | :arrow_up: | | [unit-test-postgresql](https://app.codecov.io/gh/go-sigma/sigma/pull/284/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-sigma) | `35.05% <71.42%> (+0.20%)` | :arrow_up: | | [unit-test-sqlite3](https://app.codecov.io/gh/go-sigma/sigma/pull/284/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=go-sigma) | `35.05% <71.42%> (+0.20%)` | :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=go-sigma#carryforward-flags-in-the-pull-request-comment) to find out more.

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