Fix compatibility with numpy 1.26 on i386 (Closes: #149)

[avalentino]

Restore compatibility with numpy v1.26 on i386 by explicitly using float64 in test code.

• [X] Closes #149
• [ ] Tests added
• [X] Tests passed
• [X] Passes flake8 pyorbital
• [ ] Fully documented

[codecov[bot]]

Codecov Report

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

Project coverage is 87.56%. Comparing base (18340ca) to head (6b8a586). Report is 6 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #150 +/- ## ========================================== + Coverage 87.51% 87.56% +0.05% ========================================== Files 14 15 +1 Lines 2210 2219 +9 ========================================== + Hits 1934 1943 +9 Misses 276 276 ``` | [Flag](https://app.codecov.io/gh/pytroll/pyorbital/pull/150/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/pytroll/pyorbital/pull/150/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pytroll) | `87.56% <100.00%> (+0.05%)` | :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=pytroll#carryforward-flags-in-the-pull-request-comment) to find out more.

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[coveralls]

coverage: 87.562%. remained the same when pulling 6b8a586d8db6394e80c9f363f6aafe2ed1e0038a on avalentino:bugfix/numpy_1.26 into dbabd00386c7d51108fe5527ac58978a3b160428 on pytroll:main.

[avalentino]

Unfortunately the patch doesn't work properly. Sorry for the noise