Fix classification of custom licenses in License Compliance

What does this MR do and why?

Fix for #285120 (closed)

Custom licenses that are not listed in spdx index do not appear on Pipeline Policy tab. That happens because such licenses are added to database by their name, but referenced in the scanning report by id. This MR fixes that as well as introduces small refactoring for its test suit.

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Example of the bug https://gitlab.com/brytannia/test-license-test/-/pipelines/383274955/licenses

Fix:

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Related to #285120 (closed)