[MSHADE-456] test-jar dependencies remain in POM after being shaded

**[Nick Tindall](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=JIRAUSER301869)** opened **[MSHADE-456](https://issues.apache.org/jira/browse/MSHADE-456?redirect=false)** and commented

When a shaded POM includes a **test-jar** dependency, it remains in the dependency-reduced POM despite being included in the uber-jar

Minimal reproduction is available [here](https://github.com/nicktindall/shade-plugin-test-jar-issue)

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**Affects:** 3.5.0

Start with the minimal reproduction linked in the issue and inspect how the shade plugin handles test-jar dependencies when generating the dependency-reduced POM. Done means a test-jar dependency included in the uber-jar no longer remains in that POM.

Written by the indexing model from the issue text.