On a fresh install of Debian 12, the WikiSuite installer leads to "line 1: syntax error near unexpected token"

A user report this to me by email when "running the quick and standard install script on a clean debian 12 system"

https://wikisuite.org/How-to-install-WikiSuite

~# bash wikisuite-installer.bash
wikisuite-installer.bash: line 1: syntax error near unexpected token "newline"
wikisuite-installer.bash: line 1: syntax error near unexpected token ""