FODO Channel Python w/o Slice Diags

[ax3l]

The inputs file version does not use slice diagnostics, so the Python test should set the same. Speed up by ~2.5x.

[codspeed-hq]

Merging this PR will not alter performance

✅ 29 untouched benchmarks

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_{Comparing ax3l:fix-test-slice (3b3f886) with development (b735d6e)¹}

Footnotes

1. No successful run was found on development (ab61ac8) during the generation of this report, so b735d6e was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩