Rename mock_setup_entry fixture

[epenet]

Proposed change

Adjust fixture naming for mock_setup_entry
Based on review comment #88319 (comment)

cc @frenck, @emontnemery

WARNING: this is an alternative to #88484

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• Dependency upgrade
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• Breaking change (fix/feature causing existing functionality to break)
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[frenck]

Closing in favor of #88484