Fix undercoverage for github importer specs

Carla Dragorequested to merge
582972-fix-gh-importer-undercoverage into master

What does this MR do and why?

Fixes undercoverage in Improve handling of attachment urls and filenames (!215079 - merged) and Make 4XX responses not retriable for attachment... (!214563 - merged).

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Related to #582972 (closed)

Edited by Carla Drago

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