I think not fixing this in the package as a regular fix (it's a patch after all) is ill-advised, but for those who find this bug unfixed in their installation:
The workaround is to install asciidoc through pip install --user asciidoc instead, or possibly with pipx. Example in line #6 of my test build script here: https://gitlab.com/fetchmail/fetchmail/-/commit/bf6c7b1eb8d476eb8c71419096e5f5470d205dfb#c5cb59670c749d48bf0114e280b297d49e50f3ac_0_6
