Minor refactoring around DumpPackage #3454

Job	Run time
Pedantic	4m 58s
Unit tests (ubuntu-latest)	2m 2s
Unit tests (ubuntu-latest, alpine, --docker --system-ghc --no-install-ghc --flag stack:static)	4m 45s
Unit tests (windows-latest)	4m 42s
Unit tests (macos-latest)	2m 15s
	18m 42s

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