asdf-install.lisp link is borked.
The link on https://common-lisp.net/project/asdf/#implementations with the name 'script' as in:
"To deal with an implementation that does not yet provide ASDF 3.1 or later, we provide a script that will install the ASDF from your git checkout to where your implementation goes looking for it when you (require "asdf")."
links to https://common-lisp.net/asdf/asdf/blob/master/tools/install-asdf.lisp rather than https://gitlab.common-lisp.net/asdf/asdf/-/raw/master/tools/install-asdf.lisp?inline=false