Fix incorrect Doxygen comments (practicalswift)
Pull request description:
Fix broken Doxygen comments.
This commit was taken from #13914 which now only covers `-Wdocumentation`.
https://github.com/bitcoin/bitcoin/pull/14103/commits/0e534d4dcae91ecf7ebd7a667227f7c26b4d5755
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Backport of Core PR14103