Fix incorrect generator kwargs with grid moveables

[codecov[bot]]

Codecov Report

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

Project coverage is 93.56%. Comparing base (503a105) to head (19018cb).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1036 +/- ## ========================================== - Coverage 93.60% 93.56% -0.04% ========================================== Files 203 203 Lines 13126 13125 -1 Branches 2681 2681 ========================================== - Hits 12286 12280 -6 - Misses 592 594 +2 - Partials 248 251 +3 ``` | [Flag](https://app.codecov.io/gh/dstl/Stone-Soup/pull/1036/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | Coverage Δ | | |---|---|---| | [integration](https://app.codecov.io/gh/dstl/Stone-Soup/pull/1036/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | `65.86% <100.00%> (-0.02%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/dstl/Stone-Soup/pull/1036/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | `89.19% <100.00%> (-0.05%)` | :arrow_down: | 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=dstl#carryforward-flags-in-the-pull-request-comment) to find out more.

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