CPack/Deb: Restore setting of root as the owner of files

Refactoring in commit v3.10.0-rc1~220^2 (cmCPackDebGenerator: Use
libarchive to create .deb file) accidentally broke this for the
top-level archive.
10 jobs for fix-deb-packaging
Status Job ID Name Coverage
  External
passed ghostflow-branch-check-master

passed ghostflow-commit-check

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