Use non-mock selectors in executor test

[eleftherias]

Summary

Use real repository selector in executor tests instead of mock.

Fixes #4017

Change Type

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

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Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 53.891% (+0.05%) from 53.844%
when pulling 9bf3813 on eleftherias:4017-selectors-executor-tests
into 1bcc1c2 on stacklok:main.