Sync the document store interface description

There have been some minor edits in the official version
of this in xdg-desktop-portal. Sync up the version here.

Closes: #2064
Approved by: alexlarsson
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f