Fix bug in assert_has_image_n_labels

[kostrykin]

Fix bug introduced in #17581: The argument labels was missing in assert_has_image_n_labels and is now added.

A test which covers this bug is added (fails before the fix).

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• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
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[kostrykin]

Maybe some explanation regarding the updated test:

Before, the argument labels was missing in lib/galaxy/tool_util/verify/asserts/image.py:254, and therefore exclude_labels was passed mistakenly for labels to the _get_image_labels function. Due to the structure of the test, the test passed. The test is now changed so that it fails if labels and exclude_labels are confused.

[davelopez]

Thanks for the fix!