Fix: generator adds new namespace.

[dblock]

Description

Fixes nox -rs generate by properly adding any new namespace in-place of other ones.

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[codecov[bot]]

Codecov Report

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

Project coverage is 70.35%. Comparing base (ba715b9) to head (218bc15). Report is 59 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #813 +/- ## ========================================== - Coverage 71.95% 70.35% -1.61% ========================================== Files 91 113 +22 Lines 8001 8877 +876 ========================================== + Hits 5757 6245 +488 - Misses 2244 2632 +388 ```

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