Remove excess spacing between the tab widget and the Run button

[p-j-smith]

Part of #266

• remove large space between the tab widget and the Run button

previously:

now:

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (392fbb8) 86.11% compared to head (7617583) 86.12%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #359 +/- ## ======================================= Coverage 86.11% 86.12% ======================================= Files 30 30 Lines 2125 2126 +1 Branches 394 394 ======================================= + Hits 1830 1831 +1 Misses 214 214 Partials 81 81 ``` | [Files Changed](https://app.codecov.io/gh/quantumjot/btrack/pull/359?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alan+R+Lowe) | Coverage Δ | | |---|---|---| | [btrack/napari/widgets/create\_ui.py](https://app.codecov.io/gh/quantumjot/btrack/pull/359?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Alan+R+Lowe#diff-YnRyYWNrL25hcGFyaS93aWRnZXRzL2NyZWF0ZV91aS5weQ==) | `98.76% <100.00%> (+0.01%)` | :arrow_up: |

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[deprecated-napari-hub-preview-bot[bot]]

Preview page for your plugin is ready here: https://preview.napari-hub.org/quantumjot/btrack/359 Created: 2023-08-03T14:12:52.503291